Windows 11のエラー修正方法（Windows 11向け）

# Windows 11のエラー修正方法（Windows 11向け）

### 제품 주요 사양

| Specification | Value |
|—|—|
| Platform Market Share (Desktop PCs, Global) | 72% |
| Market Share Growth (approx. 2-month period) | +22 percentage points |
| Data Source | StatCounter, 2026 |

## Why Ignoring Small Windows 11 Errors Always Costs You More in the End

Windows 11 now runs on over 72% of desktop PCs globally — a sharp jump of nearly 22 points in just two months (StatCounter, 2026). More users on one platform means more shared vulnerabilities. Whether it’s a random blue screen, a frozen taskbar, or a stubborn startup failure, system errors rarely disappear quietly. They grow. Left untreated, a minor glitch can snowball into data loss, security exposure, or complete system failure.


_{Source: https://www.pasoble.jp/imageData/windows11-update-history-check-error-code.gif}

## Blue Screens, Boot Loops, and Frozen Apps: How to Recognize the Most Common Windows 11 Error Types

Honestly, not all Windows 11 errors are created equal. Some are minor annoyances — a frozen taskbar, a sluggish boot. Others, like the dreaded Blue Screen of Death, stop you cold and take your unsaved work with them.

**Blue Screen of Death (BSOD)** is probably the most alarming type. You’ll see a full-screen blue (or sometimes black) crash page with a stop code. The ones I’ve encountered most often include `CRITICAL_PROCESS_DIED`, `KERNEL_SECURITY_CHECK_FAILURE`, and `PAGE_FAULT_IN_NONPAGED_AREA`. Each code points to a different root cause — which matters a lot before you start attempting any fix.

**Startup and boot errors** are another common category. Symptoms: the system loops endlessly at the Windows logo, shows “Automatic Repair” on repeat, or throws a black screen with just a cursor blinking. These typically trace back to corrupted boot configuration data or a failed update.

**Update errors** — think codes like `0x80070002` or `0x8007001f` — appear when Windows Update stalls mid-installation or silently rolls back. You’ll usually see a percentage counter that freezes, or a frustratingly vague “something went wrong” message.

**App crashes and freezes** look different from the others: a single program stops responding while everything else runs fine. Windows 11’s Event Viewer quietly logs these incidents in the background, which actually makes them easier to trace than they initially seem.

The symptoms tell you *which category* you’re dealing with. Get that wrong, and you’ll spend hours fixing the wrong thing entirely.


_{Source: https://www.ubackup.com/screenshot/jp/others/0xc1900101-windows-11/0xc1900101.png}

## Hardware or Software First? Preliminary Steps You Must Complete Before Any Windows 11 Fix

Before you type a single command or click anything in your Windows 11 system, stop. Honestly, the biggest mistake I’ve seen people make is diving straight into fixes without any preparation — and that’s exactly how you turn a minor error into a full data disaster.

**Step one: back up your data. Right now.** Even if it’s just your Desktop, Documents, and Downloads folders. Copy them to an external drive or cloud storage. A botched repair can occasionally make things worse, and you don’t want to learn that the hard way.

Next — and this is something most guides completely skip — ask yourself a critical question: *is this a hardware problem or a software one?* Here’s why it matters. If your SSD is physically failing, running system repair commands won’t help at all. Brien Posey, a former 22-time Microsoft MVP, makes this clear: sequential troubleshooting only works when you understand the root cause first.

**Quick diagnostic checklist before touching anything:**
– Note exactly when the error first appeared
– Did it start right after a Windows Update? That’s a big clue
– Is your PC running unusually hot?
– Any strange sounds from your storage drive?

Also, **write down your exact error code.** Something like `0xc000021a` or `CRITICAL_PROCESS_DIED` is genuinely useful — not just noise.

Finally, confirm Windows 11 is fully updated. Microsoft’s April 2026 patch addressed 167 vulnerabilities at once. An outdated system is, in many cases, already a broken one.


_{Source: https://whileint.com/ja/tech/lindsy/wp-content/uploads/2021/12/BSnuJH5I12.jpg}

## Built-In Diagnostic Tools That Fix Most Errors Without a Technician

Honestly, most people don’t realize Windows 11 ships with surprisingly capable self-repair tools already installed. No downloads, no subscriptions — just built-in utilities sitting on your machine, ready to work.

**Start with the Windows Troubleshooter.** Head to Settings → System → Troubleshoot → Other troubleshooters. There are dedicated fixers for Windows Update failures, audio glitches, network drops, and more. Run the relevant one first. It sounds almost too simple, but I’ve seen it resolve problems that stumped experienced users for hours.

Next, open Command Prompt as an administrator and run **SFC (System File Checker)**:

`sfc /scannow`

This scans every protected system file and replaces corrupted ones with a clean cached copy — no user input needed mid-scan. If SFC reports it “found corrupt files but was unable to fix some,” escalate to **DISM**:

`DISM /Online /Cleanup-Image /RestoreHealth`

DISM fetches fresh repair files directly from Microsoft’s servers, fixing things SFC can’t touch on its own.

Here’s what most guides skip entirely: on **Copilot+ PCs** in 2026, Windows 11’s integrated AI diagnostic agent can detect anomalies *before* visible errors appear. Check Settings → System → Recovery for AI-assisted options on supported hardware — it’s genuinely useful, not just a gimmick.

Finally, run **Windows Memory Diagnostic** (search `mdsched.exe`). It tests your RAM on the next reboot. This matters because failing RAM mimics dozens of different error types — blaming software corruption when the real culprit is hardware wastes serious troubleshooting time.


_{Source: https://www.actualidadgadget.com/wp-content/uploads/2025/03/Error-en-Windows-11.png}

## When Automated Tools Fall Short: Manual Step-by-Step Fixes for Stubborn Windows 11 Errors

Okay, so the built-in tools didn’t quite cut it. That happens. But before typing a single command, there’s something most guides skip entirely: **figuring out whether your error is software corruption or a failing hardware component.** This matters. Running SFC on a dying SSD is like patching a flat tire on a car with a broken axle — you’re treating the wrong problem entirely.

**Step one: identify your exact error code.** BSODs always show one. Write it down.

– **CRITICAL_PROCESS_DIED** — Corrupted system file or bad driver. Open Command Prompt as administrator, run `sfc /scannow`. If it finds issues, follow up with `DISM /Online /Cleanup-Image /RestoreHealth` to fetch clean files from Microsoft’s servers.
– **KERNEL_SECURITY_CHECK_FAILURE** — Can signal bad RAM or a driver conflict. Microsoft’s KB5077181 (February 2026) patched a GPU-triggered version of this exact BSOD — so run Windows Update first before touching commands.
– **0xc000021a** — Critical process crash. Boot into Safe Mode, then run the SFC and DISM combo above.

After commands finish, **read the output carefully.** “Successfully repaired” is a good sign. “Unable to fix some files” means don’t stop — escalate to DISM or consider a repair install.

Last step: `chkdsk C: /f /r` catches storage-level logical errors. Schedule it on next reboot and let it fully complete. In my experience, skipping this step is exactly why the same errors creep back a week later.


_{Source: https://www.windowsnoticias.com/wp-content/uploads/2025/02/Error-651-Windows-11.jpg}

## Stability Starts Here: Build These Habits Before Your Next Error Hits

Honestly, most system errors don’t appear out of nowhere. A surprising number come down to neglect rather than bad luck. Here’s what actually works over the long haul.

**Keep updates current.** The 2026 April Patch Tuesday fixed 167 vulnerabilities in one shot. Delaying those updates means your system quietly accumulates risk. Enable automatic updates and don’t ignore restart prompts — that “remind me later” button has caused more problems than people realize.

**Create restore points regularly.** Before installing new software or drivers, set a manual restore point. It takes 30 seconds and gives you an instant exit ramp if something goes sideways.

A few more habits worth building into your routine:

– **Run Disk Cleanup monthly** — temp files and cache bloat can silently destabilize the system over time
– **Check driver health quarterly** — outdated or incompatible drivers are a leading cause of crashes, especially after major updates
– **Monitor storage space** — your system needs roughly 20GB of free space to operate reliably; drop below that and you’re asking for trouble
– **Avoid third-party “optimizer” tools** — most do more harm than good, and some actively corrupt registry entries

Restarting your PC regularly (rather than relying on sleep mode) is also more impactful than it sounds. It clears memory, applies pending changes, and resets processes that tend to drift after days of uptime.


_{Source: https://elsefix.com/ja/tech/anna/content/images/2025/03/image-447-1.png}


## Stop Chasing Symptoms: Your Final Checklist for a Genuinely Stable System

Alright, let’s wrap this up. If there’s one thing I’ve learned from years of dealing with Windows errors — prevention is always easier than repair. Here’s a checklist you can actually use.

**Key takeaways:**
– Hardware failures and software corruption look nearly identical on the surface. Always check RAM and SSD health *before* running any command-line repair tool — otherwise you’re fixing the wrong thing.
– SFC /scannow patches corrupted system files; DISM /RestoreHealth fixes the repair store itself. Run DISM first if SFC keeps failing.
– Specific error codes like 0xc000021a or KERNEL_SECURITY_CHECK_FAILURE have targeted fixes — don’t default to generic workflows when your screen is literally telling you what broke.
– Built-in tools handle most situations. Event Viewer, Windows Memory Diagnostic, and the command prompt are already on your machine, free and powerful.

**Your monthly maintenance checklist:**
– ✅ Install pending updates (167 vulnerabilities were patched in one April 2026 release alone)
– ✅ Check driver status in Device Manager
– ✅ Run SFC if anything feels sluggish or unstable
– ✅ Verify SSD health with built-in diagnostics
– ✅ Review Event Viewer for warnings before they escalate
– ✅ Back up critical files before any major update

Honestly, most people skip maintenance entirely until something actually breaks. Don’t wait. Five minutes a month beats five hours of recovery — every single time. Windows 11’s self-healing features are genuinely impressive at this point, but they work best on a system you’ve been looking after.