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Fix Windows that has CPU that is at 100 percent

We'll find the process using the CPU, end it, and disable startup or run antivirus—or tell you when to call a pro.

Troubleshooting · Home maintenance
15–30 min
Step 1 of 3

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Steps

Goal: Find the process using the CPU, end it, and reduce startup or run antivirus.

  • Task Manager, sort by CPU. End the top process. Disable startup programs.
  • Good: CPU usage drops. You are done.
  • Bad: Run antivirus scan or update/reinstall the app.

Find top process

Goal: Identify what is using the CPU.

  • Task Manager, Processes, click CPU column. Note the top process.
  • Good: You see the process. End it.
  • Bad: Run antivirus—malware may be hiding.

End process

Goal: Stop the process using the CPU.

  • Right-click the process, End task. If it returns, disable it from Startup or uninstall.
  • Good: CPU drops. Process does not return.
  • Bad: Run antivirus or reset Windows.

When to get help

Call a technician if:

  • No process stands out and CPU stays at 100 percent.
  • You suspect malware you cannot remove.
  • The PC overheats or shuts down.

Verification

  • Task Manager shows CPU usage below 100 percent when idle.
  • No single process constantly using the CPU.
  • PC feels more responsive; fans quieter.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Find process Task Manager, sort by CPU; end the top process.
  2. Disable startup Task Manager, Startup, disable heavy apps.
  3. Antivirus Run full Windows Defender scan.
  4. Reset Windows Reset this PC, Keep my files.
  5. Call a pro No clear process; malware suspected.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Top process name and CPU percentage
  • Whether process returns after end
  • Steps already tried

What process uses the most CPU?

Task Manager shows CPU per process.

Task Manager, Processes, sort by CPU. Good: Normal program—end it. Bad: System process—disable startup, run antivirus.

Yes No

You can change your answer later.

Find the process

Task Manager, CPU column. End the top process. If it returns, disable startup or run antivirus.

Done

End or fix

If program: end process; update or reinstall. If unknown: run antivirus. Disable startup programs.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would CPU be at 100 percent on Windows?
A runaway process, malware, too many startup programs, or a buggy app. Task Manager shows which process.
Is it safe to end a process in Task Manager?
Yes for most user programs. Do not end critical Windows processes (e.g. System, Runtime Broker) unless you know what you are doing.
When should I call a technician?
When no process stands out, CPU stays high with nothing running, or you suspect malware you cannot remove.

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