I'm guessing that the reason you don't have any gears left is that you broke or stripped the gears on the transfer shaft or counter shaft that comes out of the tranny. 4th and 5th gears are way too strong to strip teeth given the torque ratio, it's not happening unless you have massive power and drive the car like a monkey. If you've broken off a few teeth, they may have lodged in the other gears and destroyed them though. It's possible, I've seen it done, it's not pretty.