If SFC got a lot of hits, this could be an indication of your harddrive dying.
That's a worst case scenario mind you just something to be mindful of.
Honestly since I don't know your system first hand the simplest thing I can think of at the moment that would at least remove problems with windows itself from the equation is this. Repair Install
This will reset windows to factory defaults without removing installed applications or causing the loss of your personal data. Anything related directly to windows will be reset to default though. This includes your desktop and any custom windows settings you may have.
I do suggest uninstalling your antivirus before doing this and reinstalling it afterwards if you choose to take this particular piece of advice.