Back-UPS Pro 1500VA sounds alarm and shows F07 error when plugged into wall outlet

[BitHappy]

I bought this until about a week ago or so and when I plugged it in and turned it on it started its high pitched alarm and displayed F07 on the screen, where none of the buttons worked or would do anything except turn it off if I held the power button for a few seconds. I noticed though, that I was able to turn it on fine when not plugged into the wall. On battery power, it would appear to function normally, but then if I plugged it into the wall at any point during, within about a second or so it would lock up again, giving me the F07 error and an alarm.

I checked the manual but all it says is that its related to "Temperature" but the room is neither very hot nor cold, so I'm not sure what the trouble could be, perhaps a bad thermistor? Any help would be appreciated! Thanks!