Also check your Event Viewer>Adminstrative View to Google repeat errors for a solution.
Check msconfig>Startup list for freeloaders on your RAM/CPU which dont' really need to startup until you click them. I only allow AV and gadgets.
Do you have one of the paid bloatware AV's? If so, Revo it in advanced mode to get out all traces, then install MS Security Essentials or Avast for a no-impact yet effective solution which doesn't bog your system AT ALL.
Run state-of-the-art free CCleaner "Run Cleaner" and Registry tab, followed by Auslogics Disk and REgistry defraggers monthly to keep your HD perfectly clean and ordered.
Run sfc /scannow to check that System Files are not damaged. If this persists, run a Repair Install
which is the next best thing to clean reinstall.