Try plugging the mouse into every available USB port on the computer. See if any of them work. After that, see if you can borrow another mouse to try.
This should be working, it sounds like you have either a bad mouse or a bad USB port. If you're lucky, there's just some temporary problem with that one USB port and it will go back to normal after your OS install is finished.
If all of that fails, try using the "Tab" and "Return" keys and see if that's enough to get you through the process. I don't know if it will be, but that's your best bet to try.