Check any and ALL solder points, get a magnifying glass, look for tiny tiny bits of solder ANYWHERE they shouldnt be
then, go to Radio Shack, and if you dont already have desolering braid and a low wattage soldering iron, get them. desoldering braids are amazing, but require patience. I splashed sodler all over an LPC chip in my PSone while trying to install a modchip, and the desolering braid saved my life