Did a clean install of windows 7 ultimate. After a while, discovered that CPU usage was into the 80%. No applications were running, went into performance on task manager and it showed that system interrupts was using over 80 % of the cpu. Updated all my drivers, some searches on google said it could be the graphics card. I have nvidia geforce 9100. Some said it could be itunes, so I uninstalled that. When I got frustrated, reinstalled windows 7 and did not install any additional programs. It was still doing it. All drivers were updated. Finally figured out that if I set the computer to never go to sleep, and the monitor to never turn off, the the system interrupts would not kick in and hog all the cpu. Now I have to shut down every time , or else leave my computer running full time in order for it to not slow down and freeze up.