USB Mouse no longer moves [Windows XP SP2]

I currently have a USB Keyboard & Mouse with Windows XP SP2 - and for the past year or so everything has worked perfectly fine. Then all of a sudden a few days ago my mouse stopped responding, the cursor is there but it won't move no matter what I try (no clue why this started, didn't install anything new, add any new hardward, etc...)

The joke is - the problem only seems to be USB Mouse, my USB keyboard and other USB devices work perfectly fine. I've tried a PS2 mouse and it works perfectly fine. Also tested a Wireless Keyboard/Mouse combo and the keyboard works fine but again not the mouse.

Anyone have any clues or suggestions? I would rather not go out and buy a PS2 mouse... (the one I have is borrowed).

Any help would be greatly appreciated.
Thanks,

System Restore is not enabled on the PC - automatic updates is also disabled (not on the internet) so it couldn't have been that...
In device manager there is NO mouse at all - so nothing to uninstall.
Safe mode doesn't work either (my mouse that is).

Any other ideas?
Thanks,

Works perfectly fine on my other PCs and I just borrowed a USB mouse from a friend (different one) and it doesn't work on this PC either....

I had this problem too. I think I accidentally did something after installing new hardware or software, and my BIOS changed. When this happened I was not able to use my mouse at all. Go into your BIOS (would explain, but all bioses are different..) and change the mouse to USB, then your computer will actually recognize it when it boots. If that doesn't work try a different port.