Is it the mouse, the port or Ubuntu do you think the problem is? If it is a USB mouse, plug it into a different port and jiggle the mouse. If this works, it's a problem with the mouse. Unfortunately, computers that use a PS/2 mouse usually only have one port. Try plugging your USB or PS/2 mouse to a separate computer. What mouse related results do you get? (If you use another computer, preferably use a different OS to Ubuntu.)