It's possible the switch is bad, but that's not the first thing I'd look at. To replace the topcase (which has the switch on it) requires removal of the topcase, and I believe there is an iFixit guide for that. Does it do anything at all when you power on? If not, have you tried another known-good AC adapter? I would remove the Airport, extended memory, and battery, and try to reset the PRAM and PMU, which can sometimes jumpstart a system. Also, when the AC adapter is plugged in, does it show a light on the plug, and if so what color and is it steady or flickering?