Question : System Process 95-100%

I have a clients computer (Presario SR1720NX) 512MB RAM Semperon 3500+. Client was complaining about how slow it is . I checked task manager and system process shows 95-100% ( not System Idle) I did virus and spyware checks (none) to no avail. I have backed up the drive and done a destructive recovery from recovery partition. I have up dated the BIOS and System Process still runs at 95-100%. I ran the hardware diagnostics in the PC Recovery and everything passed (CPU, Memory and HDD) I have run out of ideas! Does anyone have any more ideas?

Answer : System Process 95-100%

That's really bizarre man!  And you added no new hardware, correct?
USB is built in...i.e. not an add on card?

If you can't even uninstall it...at a minimum I am wondering if the Windows install isn't a bad one.  I don't guess you have a spare OEM CD laying around to test that theory?  Otherwise, I am really out of suggestions.  I know you could turn it off in BIOS, but that won't help a lot.