I have an interesting thing going on and I am not sure what it is. The hard drive runs all the time and after a while the computer gets really slow. Is it a hard drive buffer issue, hard drive in general or memory issues?
1. Disable any unnecessary programs from running at bootup
2. Download Ccleaner and do a custom clean
3. Download Malwarebytes and scan your pc for malware, have it quarantine anything it finds
How old is this computer?
click on the processes tab, click on the disk column so that it sorts it by highest usage first, take a screenshot and post it so we can see whats using the disk.