pc 100% disc issue - impossibly slow. windows pro 10 on dell optiplex

Hi yvonne88 and wellcome to Tenforums!

I would start with disk backup. Could be dying drive (net necessarily, but could be).

Do you have SSD? Sometimes new firmware sloves the issue.
Resetting pagefile.sys could also help.

Can you post a picture of Resource monitor with disk read write sorted?

yvonne88 said:

thank you for your response. It is all way above my head. I sorta need step by steps instructions. I just replaced the hard drive about 1 year ago.

OK, since we don't know, if disk is in good shape (you've mentioned some corrupt files) making a backup of any important data is a must.

Do you have any important files on computer?

Making system image with Macrium reflect free is simple enough to try. You'll need only part 1 and 3 of tutorials below:
Tutorials | Backup and Restore with Macrium Reflect

other steps (we can do this later...)
-checking resource monitor:

click on Start and start typing: resource monitor (recource monitor will show up .. - click on it to start is)

Check the image below and try to recreate it. Take a screenshot (press Win + Shift + S and select area to take screenshot. Paste it in here

Hi, there are many possible causes- noted System is responsible for the high disk usage.

Also noted you said

the system file checker did say that it found corrupt files and that it was able to fix some but some were not able to be fixed.

a. Please post a screenshot of your Update History.
b. How much free space do you have on C: ?

c. Please boot to Safe Mode. Check your disk usage and post the result.
Hopefully it will then be low.

d. If so, run
chkdsk c: /scan
from an admin command or Powershell prompt
and post the result. (Note this is just a test- it fixes nothing).

e. If this fails, run
chkdsk c: /f
Your PC will probably need to reboot, and this could take a long time to complete.

To examine how System is using your disk try Process Explorer (free from MS):

All good advices from dalchina…
I've noticed Firefox is very high in disk usage statistics (also response wise). Read is very high.

Clear all data from Firefox cache:

mozilla how-clear-firefox-cache

I would clear cookies too, but you would have to sign in al the pages again..

This should help for short time - enough for some repairs and scans could be done.
After it, check the system with Malwarebytes and ADWcleaner for any unwanted malware you may have.

Also, how much memory your system has? And check Task manager, if anything stands out...

Only real way around 100% diisk use is to upgrade RAM and go with a SSD. The sad thing is that your machine is handicapped with only 4gb RAM. Time to move to a machine that can handle Windows 10 better.