You have a Magnum Dimensions 400 watt pure sine inverter. Input is +/- 12vdc and a chassis ground. Output appears to be via a normal wall plug.
Magnum has a trouble shooting procedure on their web site:
Trouble ShootingI'd try that first. If it's dead they have a phone number in the trouble shooting page. Maybe they repair these?
If not I'd buy a 400-800 watt pure sine inverter woth a plug output and install in your failed units place.
Room should not be an issue because you unit is huge and it weighs 14 pounds. You'll be amazed at what will replace.