There was a warning published a while back regarding HP notebook batteries overheating. Is yours one of those perhaps?
PC Notebook Computer Batteries Recalled Due to Fire and Burn Hazards
The other reason could be spyware. Check for infection using the free versions of both of these tools and let them clean everything they find:
http://www.superantispyware.com/supe...freevspro.html http://www.malwarebytes.org/mbam.php