If this problem just recently started, you could try running a full scan with your installed anti-virus suite to rule out a malware issue. It would be a good idea to use another free on demand scanner because no anti-malware product is 100% effective 100% of the time (if there was such a thing we'd all be using it.) A couple of recommended products are:
You could also check for damaged or corrupt system files by running a system file checker scan from an elevated command prompt (option two.) If problems are found, run the scan 3 times and reboot the computer after each scan.
After you run the SFC scan, run a Check Disk scan. You could either use the elevated command prompt as above and type in chkdsk C: /f > Enter or you could use option one in this tutorial: