ph14 wrote:I've run anti-virus software: Microsoft Security Essentials and Malwarebytes Anti-Malware. Anything else I need to do?
Are any processes using tons of CPU?
Press the windows key and R, then type taskmgr in the dialogue box and press enter. Click the CPU column header to sort by CPU usage.
Do you have plenty of free space on your hard disk?
Your hard drive could be on the way out. You could download and run the Acronis drive monitor to see if there's any obvious problem there.