i think by the time you pay someone to look at it you would be better to get a new one.
there is a 30 amp unit for sale on ebay, here
you could use that for a basis on what a replacement might cost.
however, there is still hope. the 74 excella that the unit in this post was installed has the univolt powered on the GFI circuit. it shares about 4 to 5 other outlets. when we went to power it up we found the GFI tripped from the exterior outlet being damp.
have you tried the univolt on a seperate circuit?
if it is junk toss it, but you might kick yerself if a new inverter snapped the breaker too!
can't hurt to try it plugged into a different source, just be careful!