I've tried selecting at least a dozen dates using the Windows facility (Start/Help&Support etc) to restore my system following some very odd stuff going on, but everytime it tells me it can't restore to that point !!
The odd stuff going on could be down to spy/malware which in some cases sits in your "system volume info files" which is where your restore points are kept, i would scan your PC for this with what ever progs. you have.
Unfortunately it will not remove any issues from within system restore you will need to turn it off to delete these files and as yours does not work you might as well...
I know this doesn't help your immediate problem, but the long term solution is to have a second (external) disk and use imaging software (such as Acronis True Image) to make complete discrete backup images (i.e. not incremental images).
My personal view is that such a course of action is the single most valuable thing that a PC owner can take.
It provides a fallback against a multitude of sins (e.g. malware infections, hardware failures, user incidents, faulty software updates etc. etc.).
For the relatively small cost involved I cannot recommend it highly enough for the lack of stress it engenders.