Go to Start and type in "devmgmt.msc" (without the quotes) and press Enter
Are there any problem devices noted there?

If not,
Click on the "Mouse and other pointing device" category to expand it.
Right click on your Mouse and uninstall it.
Reboot the computer and let Windows redetect the mouse.

If it's still acting funny - then try another mouse.
Test either with another mouse of the same type (PS2 or USB)
or Test with another mouse of a different type (PS2 or USB)
That way, if problems continue, you'll have started troubleshooting the connectors on the mobo.

 

if its a laser mouse it might be dirt in front of it
lint/fluff also lets my mouse move on its own