This may come as small consolation to anyone having this issue, but I also had the problem, for several days- just before the drive failed. SOLUTION- SSD, which has finally become reasonably priced, I swapped out my Dell's sad, old school mechanical disk for a similarly-sized SSD, and my drive usage went down to almost nothing. Now, the bulk of the usage is on the memory and CPU, and not on the hard drive. Hallelujah! I can't say for sure that the swap was the solution, or that my 100% usage wasn't related to the state of the failing drive. All I can say is, well. Problem solved.
Incidentally, I went through EVERY recommended fix, turning things off, standing on one leg, saying a prayer, but finally got resolution with the drive swap. So, I got that goin for me.