It seems unlikely but you didn't install the multiuser stuff did you? I had a system that behaved exactly as you describe... the process that was using the CPU was ssesctl.exe part of the multiuser stuff. Does that slate have hyperthreading? If it does can it be turned off?
http://bugs.ecomstation.nl/view.php?id=2132
http://bugs.ecomstation.nl/view.php?id=2132