I am having the same problem and it doesn't go away even when I change os from win 10 to 8.1 ....
I encountered this issue when my pc crashed and a BSOD showed up saying unmountable harddisk I had to reformat the harddisk which didn't help and when it finally booted I had stuck with this 100 % disk usage ...no programmes using more than 0.1 mb of harddisk and yet 100% usage ....disk monitor didn't show any apps using it till that high plus i tried al, the fixes on internet like disabling winsearch, superfetch and BITS BUT NO SOLUTION.....at last I wanted to reformatt it again and now it says the selected harrdisk space cant be used .., the volume is offline , I tried diskpart but it returns the error could not online the selected volume......haven't found any solution yet .....can anyone help....I use an i5 ,8gb ram,1tb hdd,