Recently I was having issues with Win 10 freezing randomly, I went through almost every repair option mentioned here, but little luck. And, like others have mentioned, I was having difficulty getting System Restore to work. It launched and ran well enough, trying to restore to a point I knew was good, as I had only created it within the last three days, but after finishing it's task, system restore reported "unable to restore, your machine remains unchanged..." you know the line. Ran all my clean and repair tools in Safe Mode, disconnected all peripherals, disabled all anti-malware on the chance they might be conflicting even though there is only one anti-virus, the rest are all anti adware and suchlike. Still no luck. Ran Restore many more times, system went through the motions of restoring, but always finished with "unable to..." Without going into the details, I got the machine as clean as I possibly could without a total wipe and clean install, which I was unwilling to do. To get to my point on this, I had it more or less running properly, although still with some hiccups, so I decided to let the restore operation rest for a while until I could figure out why it was working-but-not-working, so to speak. I began to reconnect peripherals, I had to try to get along as well as I could until I came up with a permanent solution to the problem.
The last thing I re-connected was a USB one-terabyte external drive I use for incremental backups.
Lo and behold! Everything now worked perfectly, and still is after nearly three days flawless performance!
Now, I'm no tech, I have no idea what or how, but Windows seemingly needed something from that backup drive. I'm sorry I haven't a clue what it needed, or even if it actually did need to access that drive, but I'm just throwing this into the pot because whatever it was, reconnecting my backup drive seemed to fix my problem.
I know it's usually wise to disconnect external drives when troubleshooting and repairing, so as not to spread any "bad stuff" any further, but perhaps there's a scrap of something sys restore needs on that drive, as seemed to be the case for me. The tech experts here can set me straight, if they wish, I'm always open to learning, just wanted to offer my two cents.