Your post didn't give me any clue what it is this time except it seems to be in any OS. The HDD or other hardware is now suspect.
I have an HP all-in-one desktop running Win 7 with AMD Athlon dual core chip running at 1.5gh, 8 meg of memory. There is 365 gig of hard disk free space left on drive C. I installed Win 10 early on but removed it a week or so later due to some minor issues and finding it not as easy to use as Win 7. Admittedly, the PC is getting on a bit now but until recently has provided a good back up to my much newer laptop. Since I reverted to Win 7 the machine has started using close to 100% of CPU virtually all the time, even when there are only a couple of programs running. I have looked at Task Manager and Resource manager but cannot really see what the cause is. Has anybody encountered this problem and maybe found a solution? I use AVAST anti-virus and at times this seems to grab a lot of the CPU - why?