Sounds like it could be a virus/malware infection using up your system resources.
Hold down the power button for roughly 10 seconds to force a shutdown. When you start the computer back up, try going into Safe Mode with networking (if you can). When the computer is powered back up, scan your computer for infections. Personally, I use AVG and Malwarebytes.
free.avg.com
www.malwarebytes.com
Both offer free software.