The ram in your compactor wouldn't be uneven unless something else had also gone wrong. The left and right sides of the ram are fastened to steel power nuts that ride up and down on two power screws. The bottom end of those screws end in sprockets connected to each other via a chain. Since that ram was, once upon a time, level, either the ram itself has bent (unlikely) or one side has slipped relative to the other.
Pull the compactor out, disconnect the power, and remove the top cover and motor cover. Look at everything you see here: broken, bent or loose parts. You may be able to rotate the motor to raise the ram and get the trash drawer out. If not, you'll need to turn the compactor on its side and remove the bottom panel, which is where you'll find the gears, chain, and sprockets. Inspect these carefully: is the chain loose enough to slip? Are teeth missing on any of the sprockets? Is the main (plastic) drive gear cracked? If you turn the motor by hand, does everything move correctly?
If you need to remove or adjust the chain, loosen the bolts holding the motor/drive gear assembly. The motor can slide enough to slip the chain off of the sprockets. With the chain off, you can rotate either power-screw sprockets independently and level your ram out. (You could also level the ram by raising it more; the "high" side will top out first and the ram will level itself, but this "fix" doesn't answer the question of how your compactor got this way in the first place!)
The most difficult repair will be if the power screws or power nuts are worn out (or stripped); that's probably the point at which I'd consider a service call (or a new compactor, which may not cost much more than those parts!)