I am having the same problem. Win 10 was installed by MS over the top of Win 7 (3x now) with the promise of a fix. Various applications go into a not-responding situation and each time the disk light is on solid. It appeared to be Defender causing the problem so I installed a different one where I could control the schedule of the scans, and disabled defender. While it seems better the disk light comes on solid and nothing works until it goes off. I must have contacted MS at least 10 times on this issue and still not be able to get it fixed. I checked the disk for errors and for viruses (using 2 different AVs) to no avail.
All of the available maintenance has been applied. The system is about 6 y/o and the vendor, HP, has not certified it ( a laptop) for Win 10 and there are no drivers that are specific to Win 10 available. The Bios is up to date. I've attempt to find out what service is causing all of the IO through the process explorer, but still have not found the culprit.
Anyone have any suggestions? MS wants me to up-date my 8.1 Pro system to W10 which I refuse to do.