lol, overconfidence is a bitch. My suggestion is to check in between the pins and behind them, take a look at the solder pads, make sure there isnt a TINY small bridge on one of the pads with the solder in the back. I cant TELL YOU how long it took me to find it, and this was after I decided to trash the 128 upgrade and was when i had the chips all removed from my first board. dont just look at the front of the pins, look at the WHOLE solder pad, and like everyone else said, make sure all your points are connected solid =)
Good luck