GRRRR this is driving me insane!

I found a USB mouse in a cupboard the other day, plugged it into my system and suddenly lost all my motherboards USB. Ive assumed that the mouse must of had a short on it or something, and has blown up my onboard USB controlled.
Well being a tightass uni student, instead of replacing my motherboard. (a Gigabyte GA7N400 - L1), i opted to make use of one of the 5 pci slots i have, and bought a cheap Via PCI USB card. Ive disabled the onboard ports in Bios to avoid conflicts, Im running the latest Mobo drivers, Windows XP Prof service pack 2, turned off Power saving on all USB devices, Installed the USB Filter driver, Put it in different slots and generally pulled my hair out.
What the problem is, is that the USB will work, but then disconnect itself. Eg; The mouse will disconnect, and the only way to get it working is to unplug it and plug it back in, where it is recognised again. When im printing, My printer will print half a page, then stop because its been disconnected. My USB drive will sometimes transfer files, but then stop halfway.
The System I have is as follows;

GA7n400-L1 Mobo
Seagate 120gig hd 8mb cache
radeon 9500 Pro vid card
Pioneer dvd burner
Pioneer dvd reader
512 meg ram, D/C
XP2500+ CPU

Ive never had a problem with this system till now, and this problem is irritating the hell out of me!

Actually another thing ive noticed (maybe completelly unrelated), is that my dvd readers light is occasionally just barely on even when the drive is at idle. Maybe its always been like that, i dunno.

Please Help!!!!!