Directly after I updated to Windows 8.1, my Lenovo AIO started slowing to a crawl. It would fluctuate between 60% and 100% disk usage, even when I wasn't doing anything.
Searching was painful, opening apps was painful and you could tell when it was running at 100%.
I read online a few different people having issues with the Skype App - since I don't use it, I simply uninstalled it. They reported that if you simply open it, the issue dissipates.
Other suggestions were:
Disable windows search - I tried that but it did not help, plus I use it...alot.
What finally did it?
Disable and remove all the apps that are pinned to your start menu that contain "live" data (the live tiles). I actually went ahead and uninstalled them, since I don't spend much time on the start screen anyway and if I'm there, it's not to read live tiles, it's to open an app.
So far, it's been running between 3 and 8 %.
Fingers crossed, I really didn't want to have to reimage my entire computer.
Update: 11/10/2015 - It didn't work. See post here for resolution.