1) Try fixes here for known issue of 100% disk usage:
https://www.lifewire.com/fix-disk-usage-windows-10-4583918
https://www.cleverfiles.com/howto/100-disk-usage-windows-10.html
https://www.makeuseof.com/tips-fix-100-disk-usage-improve-windows-performance/
https://www.reddit.com/r/Windows10/comments/nf4whm/windows_10_100_disk_usage_issue_solution_1000gb/
https://www.technology.org/2019/07/07/how-to-fix-100-disk-usage-in-windows-10/
https://www.kapilarya.com/fix-windows-10-100-percent-disk-usage-problem
2) Update your drivers from the PC or motherboard maker's Support Downloads web page, using the full model number, Serial Number or Dell Service Tag on sticker.
Compare the latest drivers available for download with the ones presently installed in Device Manager reached by right clicking the Start Menu. Make sure you have the latest BIOS or UEFI firmware, Chipset, Display (Video), Sound, USB3, Bluetooth, Network and all other drivers, or else download and install the latest now.
3) Go over this checklist to make sure the install is set up correctly, optimized for best performance, and any needed repairs get done: http://answers.microsoft.com/en-us/windows/wiki/windows_10-performance/windows-10-performance-and-install-integrity/75529fd4-fac7-4653-893a-dd8cd4b4db00
Start with Step 4 to turn off Startup freeloaders which can conflict and cause issues, then Step 7 to check for infection the most thorough way, then step 10 to check for damaged System Files, and also Step 16 to test a new Local Admin account. Then continue with the other steps to go over your install most thoroughly.
4) If this was caused by Windows Update(s) then you can check which were installed at Settings>Update & Security>Windows Update under Update History, then uninstall them from the link there, and immediately check for these again and hide with the Hide Updates tool explained here: https://www.howtogeek.com/223864/how-to-uninstall-and-block-updates-and-drivers-on-windows-10/
You can also use System Restore from within Windows to get back before the problem began, then check for Updates with the Hide Update tool and hide them: https://www.windowscentral.com/how-use-system-restore-windows-10
5) If this was caused by a Version Update then for 10 days you can roll it back in Settings>Update & Security>Recovery and then hide it until it matures using the Hide Updates Tool which is explained more here: https://www.howtogeek.com/223864/how-to-uninstall-and-block-updates-and-drivers-on-windows-10/.
If that doesn't work you can also Go Back in Repair Mode as shown here: https://www.tenforums.com/tutorials/2294-advanced-startup-options-boot-windows-10-a.html
6) If nothing else helps you can run a Repair Install by installing the Media Creation Tool and choosing from it to Upgrade Now. This reinstalls Windows in about an hour while saving your files, apps and most settings, solves many problems while also bringing it up to the latest version 1909 which you need anyway and by the most stable method. http://windows.microsoft.com/en-us/windows-10/media-creation-tool-install
7) Test the hard drive or SSD with diagnostics: https://www.lifewire.com/free-hard-drive-testing-programs-2626183 https://mashtips.com/ssd-health-test-and-performance-monitor-tools/ HP and Dell have hardware diagnostics triggered by tapping the ESC or F12 keys respectively as you power on. Best is to use the HDD/SSD manufacturer's own if there is one, otherwise use Seatools bootable long test: http://blog.nowherelan.com/2013/04/04/boot-seatools-off-of-a-usb-drive/
Follow this up with a full Disk Check from the Command Prompt in Repair Mode or from bootable media: https://www.groovypost.com/howto/check-hard-drive-fix-failures-windows-10/ if necessary from the Command Prompt at boot: https://www.tenforums.com/tutorials/2294-advanced-startup-options-boot-windows-10-a.html
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But remember that in Windows 10 everything depends upon the quality of the install, and Factory or Upgrade installs are inferior installs which most enthusiasts won't even run because they'd expect endless issues. Consider now or later doing the Clean Install in this link which compiles the best possible install that will stay that way as long as you stick with the tools and methods given: http://answers.microsoft.com/en-us/windows/wiki/windows_10-windows_install/clean-reinstall-windows-10-upgradefactory-oem/1c426bdf-79b1-4d42-be93-17378d93e587
Make it a diagnostic install by monitoring for the issue after you reinstall each app, Update, settings or any modifications. Have System Restore points set so you can roll back before the change that causes this, if you isolate it.
If you were referred here from another thread, please post back results in that thread. Otherwise you can ask questions and share information in the Comments section below.
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