Computers run slow for a few reasons. The FIRST thing you want to do is the easy things.
B4 you start, define WHEN it runs slow. On boot, on the internet while browsing, when running a specific app…..
1st - run TFC - download and run from desktop = this cleans out temp files, caches, etc. Some malware might be residing there.
2nd - run CHKDSK = open a CMD prompt and type CHKDSK C: /f = scans your HDD for errors. A major cause of slowness.
When you run this it will ask if you want to run it after a reboot. Answer yes and reboot. If you have other partitions/drives do the same for them (change drive letter). They won’t require a reboot.
If you just want to see if there is trouble on C: do not enter /f and it will run without a reboot and tell you if there were any errors. You then need to run the /f to Fix the errors.
3nd - run SFC = in the same command prompt type SFC /SCANNOW = this will fix any system file errors
If it comes back saying it found errors and could not fix them, then you will need to run DISM
You must be online for this to run
DISM.exe /Online /Cleanup-image /Restorehealth
All of these will take a long time, especially CHKDSK if it finds errors. Just wait for it. I have had it take all night to finish.
At this point, test it. If it is still slow you need to run a complete AV scan.
After that, if it is still slow, boot in safe mode to see if it still runs slow. If not, then you have an app that is using a lot of resources.
Open Task Manager to see what it might be and close any that are using a lot.
If it is still slow, a RAM upgrade might be needed. This would be indicated if it runs slow with your browser or other app.
Lastly, an upgrade to an SSD will help.