Just as a check, Ctrl, Alt, Del, key all together.
Start the task manager, and have a look for these in the processes tab of windows task manager.
Stdrd.exe or Mediacentre.exe.
If you find these take a note of how much cpu time they are taking up. It is Malware and very sneeky and takes up alot of the Cpu cycle time. To remove it use Malware antibytes.