|Could you check for us if you have 100% cpu load?|
You can do this by opening taskmgr.exe, or cmd.exe if you can :/
If taskmgr doesnt work try this command in cmd.exe:
WMIC CPU GET LoadPercentage
You should also be able to tell if its under a heavy load if the fans are spinning loudly.
Though if your cpu has multiple cores, for example 4, it might only show a 25% or 50% constant load.
If the cpu is indeed under a heavy load, even tho you are not doing anything, then its likely malware like Jeff Root said in post Re #2
Simple solutions are often the best