I had the same problem. I noticed it because my case fan is loud, and normally it stays off with the PWM control settings I have. A few weeks ago it started up about a minute after boot, and then I noticed the computer seemed sluggish. The task manager showed about 50/50 "system idle"/"system" time with no programs running. Another weird problem was that 'FOX ONE' or any other software that measured CPU/system temperatures would cause XP to crash after a few seconds. The temperature would fluctuate wildly and the overtemp protection software would shut it off. XP would no longer automatically go into power saving mode. I've got a 'white box' Foxconn A7GM-S/AMD7750, but I don't think this problem is specific to this board or CPU, both of which I like a lot.
I looked for viruses (none), updated all my drivers, flashed the latest motherboard BIOS, disconnected all USB devices, removed a RS232 PCI board I had just installed, and used MSCONFIG to shut down a few startup items. Nothing helped. ProcessExplorer (thanks Mark Russinovich!) showed Hardware Interrupts at ~5% and Deferred Procedure Calls at ~10%, which is an important clue. This made me think it was a hardware problem, so I unplugged and re-plugged all of the connectors including reseating the CPU, rerouted some cables, took out the CMOS battery and cleaned it with an eraser. After this, the problem disappeared. I suspect the problem was the IDE DVD cable, but I'm not sure.
What a difference! The computer is fast again, and the fan is quiet. FOX ONE works with no problems. The System Idle process occupies >95% of the CPU time. Give it a try.
High "System Process" CPU time fixed
Linear Mode
