If it's a USB mouse and your PC has an old PS2 connection, try a USB-PS2 adapter.
If it's a PS2-mouse try a USB mouse
If it's a USB mouse, try it on another USB port
If it's a USB mouse, try another mouse (but you say you already did and it didn't work)
Do other USB devices work on that same port?
Finally, make a Linux disc or stick (that's free), boot from it and see if the mouse works there.