UPS’s dieing from Power Outages?

I have a strange problem. One of the bigger (granted still a home sized unit) APC UPS’s that we use in the office is… well… dead. It powers on and works but is stuck on “battery power”. No matter what I do with the unit, when its plugged in it still thinks its on battery power. Sadly I think I’m going to have to call APC. I hope they can do something about it – because I dont know where the recipt for the unit is (probably the CPA has it somewhere), so I can’t get it warrantied.

Shiny.