There are a few things you can try to fix 100% disk usage:

1. Restart your computer. This can often fix minor software glitches that may be causing the problem.
2. Check for updates. Make sure that you are running the latest version of Windows and all of your installed software.
3. Disable startup programs. Startup programs are programs that start automatically when you turn on your computer. Some startup programs can cause high disk usage. To disable startup programs, go to Task Manager > Startup and disable any programs that you don’t need to start automatically.
4. Run a virus scan. A virus or other malware infection can cause high disk usage. Run a full system scan with your antivirus software to check for and remove any infections.
5. Run a disk check. A disk check can scan your hard drive for errors and fix them if necessary. To run a disk check, go to File Explorer > This PC > right-click your hard drive > Properties > Tools > Error checking > click Scan drive.
6. Disable Windows search. Windows search can sometimes cause high disk usage. To disable Windows search, go to Services > right-click Windows Search > Properties > Startup type > Disabled.
7. Increase your virtual memory. Virtual memory is a portion of your hard drive that Windows uses as RAM when it needs more memory. To increase your virtual memory, go to Control Panel > System and Security > System > Advanced system settings > Performance > Settings > Advanced > Virtual memory > Change > uncheck the box next to Automatically manage paging file size for all drives, select your hard drive, and enter a custom size for your virtual memory.
8. Upgrade your hardware. If you have an old or slow hard drive, it may not be able to keep up with the demands of Windows 10. Upgrading to a solid-state drive (SSD) can significantly improve disk performance.

If you have tried all of the above steps and the problem is still persisting, you may need to reinstall Windows.