Microsoft Windows Error Code 0xC0000420: How to Fix It

Medium 1-3 hours (depending on tests) Critical Severity Verified June 2026
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Error Code
0xC0000420
Brand
Microsoft Windows
Product Type
operating_system
Severity
Critical
DIY Difficulty
Medium
Estimated Fix Time
1-3 hours (depending on tests)
Error 0xC0000420 indicates a critical kernel assertion failure in Windows. This typically occurs due to corrupted system files, faulty hardware (especially RAM or hard drive), or problematic drivers. Your system may fail to boot or crash with this error. Don't worry—follow the steps below to diagnose and resolve the issue.
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Tools You'll Need

How to Fix Error Code 0xC0000420

  1. Perform a Clean Boot

    If you can't access Safe Mode, you may need a Windows installation media.

  2. Run System File Checker (SFC)

  3. Check Disk for Errors

    Back up important data before running CHKDSK if possible.

  4. Test RAM for Faults

    MemTest86 may take several hours. Ensure the PC is plugged in.

  5. Update or Roll Back Drivers

    Only download drivers from official manufacturer websites.

  6. Use System Restore

    System Restore may affect installed programs.

  7. Reinstall Windows

    Back up all important data before reinstalling.

Parts You May Need

RAM (if memory test fails)
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Hard Drive/SSD (if disk is failing)
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RAM (if memory test fails)
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Hard Drive/SSD (if disk is failing)
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RAM (if memory test fails)
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Hard Drive/SSD (if disk is failing)
Check Price on Amazon
RAM (if memory test fails)
Check Price on Amazon
Hard Drive/SSD (if disk is failing)
Check Price on Amazon
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When to Call a Professional

If you are unable to boot into Safe Mode, cannot access the recovery environment, or your hard drive shows physical errors (clicking sounds), seek professional data recovery or repair service.

Frequently Asked Questions

What causes Windows error 0xC0000420?
It is typically caused by corrupt system files, faulty RAM, a failing hard drive, or problematic drivers that trigger a kernel assertion failure.
Can I fix error 0xC0000420 without losing data?
Yes, if you can boot into Safe Mode or recovery environment. Steps like SFC, CHKDSK, and System Restore can often resolve the issue without data loss. However, if a clean install is needed, data may be lost unless backed up.
How do I create a Windows installation USB?
On another PC, download the Windows Media Creation Tool from Microsoft's website. Run it and select 'Create installation media'. Choose USB flash drive (at least 8GB) and follow the prompts.
Is error 0xC0000420 a hardware or software problem?
It can be either. Software corruption (system files, drivers) is more common, but faulty hardware like RAM or hard drive can also cause this error.
Will resetting Windows fix error 0xC0000420?
A 'Reset this PC' option (keep files) may fix it if the issue is software-related. A clean install is more thorough but will erase all data.

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