Sounds like a tooth has broken off and jammed in the box somewhere, resulting in both being unable to select gears AND the box jammed up. Sounds like a new gearbox is needed, but one thing you could try is to tow the car backwards and forwards in an effort to get the broken tooth out. Then hopefully it might work its way to the bottom, be able to come out via the drain plug, and leave you with at most one gear not working. Good luck if that gear, is reverse or first though. You'll probably cope for a little while if it were one of the others.