use the ctrl alt delete function and see how the ”performance” is running……will tell you if the processer is pulling it’s guts out or it’s just on a go slow
You’ve checked that ‘no’ unauthorised processes are running?
Whats the bandwidth from your isp, imbetween the lines are you saying if you open a folder on your desktop it takes ages . . . . try defragging or a disk clean up (as a start)
how old is the computer and what’s the system?