Ok there are a couple things you need to look for. I know you said that you took the engine out of the buggy, so will it not roll with it in or will it also not move with the engine removed? If it wil not move either way you obviously have something caught up somewhere. Have you disassembled and reassembled any other part of the buggy since the crash? If so make sure that all the screws got put back in the correct place as my neighbor put loo long of a screw in one of the wheel hubs causing the buggy not to roll.
If non of the previous are your scenario you will just have to start looking for the culprit by moving various parts by hand. Start at the center diff and see if it will turn both the front and rear driveshafts. If not you either have something stuck in the center drivetrain or the pinion/ring gears on the front or rear diff may be binding due to a broken tooth on one of the gears.
Another thing is to leave the back wheels on the ground and spin one front wheel. If the other wheel spins the opposite direction of the one you are spinning you will know that the internals of the front diff are in worling order. Once this is finished you can do the same with the rear wheels/diff. Other than these few tests the next best way is to tear it apart and see what you find.