Can you describe exactly what doesn't work? I (or other Amiga users here) might be able to help. If it fails to boot does it give a coloured screen? IF not does it just sit at a blank screen?

If it has been moved any distance it's worth popping the lid and making sure the Warp Engine is sat in the Fast Slot (CPU slot) properly. They do wander about a bit. Also does it have any IDE devices attached? If not you might have to wait up to a minute (including the SCSI delay for the Warp Engine also) before it starts to boot.

Warren Block's FAQ for the 4000 might also provide some useful tips:

http://wonkity.com/~wblock/a4000hard/main.html