|If this happened recently and you have an idea when it might be simplest to run System Restore, which will keep your own stuff. It usually goes very well - you just sit back and wait for it to finish. You choose a restore point with a date before it happened.|
This might seem a bit ambitious for what could appear to be a simple fault but these intermittent things can be a devil to fix so it's often the best way.
Always pop back and let us know the outcome - thanks