Originally Posted by Ya_know
PS2 or USB? Which ever you have, try the other input type.
Also, have you ruled out a keyboard issue as well? You may want to try another keyboard.
This could also be spyware or a virus, but if you can't function in windows adequately it's hard to scan or remove anything like that. If you disconnect the mouse entirely, and boot with just a keyboard, no mouse driver should load. Then you can function with just the keyboard, but it takes some previous keyboard navigation experience to pull that off smooth…but you might be able to work some, and try to scan for malicious programs…
Also, since the Mobo upgrade, did the system ever work normally? If not, bingo. You may need to reinstall or at least repair windows...