I've had same trouble for about 2 months.
Then, as I was recently downloading an upgrade for Windows Media
Player, I noticed a message during installation process, that said I
would not be able to use any 'restore points' after that download - -
- UNLESS I downloaded 'Window Fix: Q290700' prior to the M P download.
This then allows me to restore back to the date of this Windows M P
version - - but not to anytime before that date!

(Easy to miss seeing this note on the way through the download
process.) Cheers!