I have been having this issue for a while. I have a PC laptop running Windows 10 and Photoshop latest. It is over 4 years old, and has 16GB of RAM. Its hard drive has 642GB free out of 917GB. The last time I shut down was just before posting this thread. I run a cleanup program about once a month.
My disk usage stays at 100%. I did a lot of things including but not limited to disk fragmentation, cleaning HD, following MS instructions available on their website for 100% disk usage issue and what not. It fixes itself for a while, which means I start computer and leave it alone for 30 mins, and disk usage goes down to about 40%. I replaced battery too, this last weekend as it started giving me error and the laptop wouldn't work without being plugged in. However, the disk usage stays the same. Now its not even going down after 30 mins. the startup programs are nearly all gone too and for the life of me i cant figure out what could be wrong. Attached screenshots were taken just a few seconds apart and show different programs being on top of disk usage. Is running a car over it the only option, because the programs aka PS takes ages to open at this level. But I will be left without a laptop to do anything. Cant afford a new one. On forums it looks like a known windows issue and i have used all methods recommended by MS to fix it but nothing has changed. Please help!