Could be a dead power supply, check the voltages or switch p/s with a working machine. Remove that fuzzy battery pronto, and thoroughly clean/douse with isopropyl alcohol. Check for trace damage around the battery, especially near SuperDenise. Other than that, gently push down/reseat all your dip chips, including the ram chips (but use electrostatic precautions before, of course). Check also the floppy and harddrive cable connections so they are seated properly.
