Hmmm... There has to be something serious wrong for the power light not to come on at all. Did you check the solder pads around the power supply connector? Perhaps it's been abused... Or maybe a burnt trace carrying power, should be fairly obvious if it's on the top or bottom layers. If you're handy with a multimeter, the schematics are available, and you might carefully check for the presence of +5V and +12V at key points (e.g. floppy connector, filtering capacitors etc.)
Edit: Of course, if you haven't done so already, you'll need to remove the shielding altogether. Anti-static precautions and usual disclaimers etc...
