Is your GFI part of an electrical panel and looks like any regular circuit breaker but with a "test" button or is it a type that looks more like a socket (except it has a test button) and installed on a wall?
You said you tried different socket in the house and it all did the same thing. Were all other circuit breakers GFI type also or did non-GFI type tripped as well?
Is your plug 3 prong type or 2 prong type? (in other words, is there a round ground pin?)
It's a socket GFI installed in a wall. I tested it on 4 different outlets, on 2 different circuits. All of the outlets were GFI-installed. The plug is a 3-prong type.