I bought a used TI Nspire from a friend who claimed it worked last semester. When I finally replaced the batteries, I was able to turn it on and use the touchpad, but none of the buttons seem to work, I can't even type a simple math problem in the sketchpad calculator. I found a new touchpad online for cheap, but I don't wanna spend the money if that won't fix the problem. Any input would be greatly appreciated.

If you have the Nspire with the removable keypad, I would try to find a friend or teacher that also has one. Try their keypad in your calculator. If that fixes the problem, then you probably need to get a new keypad. I would also make sure that the contacts are clean and free of debris.