May be you have a virus which forces CPU to work harder. Try to scan computer with antivirus programs, few different antivirus programs - there are free on the internet: Zonealarm, Malware, etc. or there are free trial (Kasperskiy, Norton, McCafee, etc): use it few days and then cancel (in ? 30 days or less) and your money will be returned to you.
Or open Task Manager and look at program component which takes most of CPU use: there can be "svchost" - windows component which takes 99% of CPU or something like that. Click on it and click on "End Task" to stop it.
Other thing is - may be your battery is not good: may be it has higher voltage than suppose to have. For example you bought new battery recently - and if not from manufacturer and is generic then it is very possible.
Or your power supply now is not good - makes higher voltage. Try good one at store.