dead battery!?!?!?!?!

i own a 92 si, when i bought it i had to replace the old battery for a new one, all ive had time for is too install a sound system. I recently went out of town for a week and had to leave the car in the garage. When i come home, the battery was drained, not even enough power to light up the green light around the ignition!!! I dont know what happened because the battery was only 2 months old!!!! i need help, what could have caused this?? n e help would be appreaciated.

simplest explaination ...did u leave anything one?

no, everything was off, excep for my amp, but i was told that it wouldnt drain the battery

im not sure about this but wat if theres a grounded wire or sumtin (maybe with ur sound system) iono just sumtin i was thinking

yeah, i guess that could of done it, its got to the shop for a checkup, i guess ill find out when that happens,