First of all, have you looked at the remote display on the side of the bed frame to see if there is a legitimate reason it has shut off power. It is supposed to do that if it detects a problem. Examples might be open ground, open neutral, etc. But if it has not shown a valid error code, then it is probably failed, as have many others of that vintage. Mine went out in late 2008.
The simple answer is to replace it, but AECS is no longer in business. Surge Guard sells an almost identical unit (they bought out AECS). The model 40250 is equivalent to what you have and is essentially a bolt-in replacement except that you will also need a new remote display (the monitor mounted on the side of the bed). The old display monitor won't work with the new unit. The good news is that its a much better remote, display voltage and current at all times and giving status messages in readable English instead of cryptic codes.
Depending on what went wrong, yours might be repairable. If its a relay failing to close or open, they can usually be replaced. But if it is giving a false error like Open Ground, then the circuit board is bad and its a throw-away.
http://www.trci.net/products/surge-guard/transfer-switches/50a-plus-hardwire-