Before you format your computer, check for the number of processes running on the background (Taskman.exe). If you are over 50 processes, try closing down the ones that you don't require.
Also take note, for any particular process that may be hogging the CPU resources. In most cases, this will be the likely cause of slow performances.
If that doesn't work, try rolling back any drivers, you have updated recently, and see if that makes any difference.
Let me know how you go.