Boot Problemm, USB?

Hi all, had a problem with my pc this evening. Was surfing the net and pc was getting slower & slower. Restarted pc and couldn't hook up to the net at all. Then got a message saying "A USB device has exceeded the power limits of its hub port. Please click on message to fix this problem." Unfortunately couldn't do anything as system totally froze. Eventually pressed reset and now PC won't boot at all. Getting power (light and fans on) but doesn't sound like HD spinning and absolutely no video signal.

I'm hoping i haven't fried my motherboard, but has anyone experienced this or have any clues? I did have a few things plugged into the usb slots, but all were externally powered except for a cellphone (was gonna download some songs to it) and my usb mouse. Have tried restarting with all usb items unplugged but it doesn't seem to make any difference.

Oh yeah its a systemax desktop P4 with 1GB RAM, Nvidea graphics PCI card, M Audio Delta 66 Soundcard, XP SP 2 etc. I do have proper tech specs around somewhere, i'll post em as soon as i find em.

Thanks in advance!