Problem with A8N5X and SP2

Heya,

As the subject states, I'm having a bit of an odd problem with my mb, a A8N5X nForce 4 S939. Normally everything runs pretty smooth. Normally I run XP with SP1 though. When I upgrade to SP2, something strange happens, as it seems suddenly my USB ports loose their connection, resulting in a loss of functionality on my mouse and keyboard - and everything else I connect to any USB port, for that matter.

Go back to SP1, everything works. I need SP2 though, and even though I do realize my MB is kinda oldish, I'm hoping someone around here will have tried something similar and can whip up a solution - or at least a few suggestion of what I must try :-).

Thanks in advance!