I just picked up a 512 from a thrift store for $15, without a keyboard or mouse. I get it home, plug it in, and turn it on. The screen flashes the happy mac and then goes blank. The drive looks like it's trying to work but I can't really tell, and there's no beep. I find a paperclip and hit the interrupt switch, and first I get the happy mac, then I get the 0f000d code ("hey stop pressing that button there's nothing wrong"). Now, after I let go of the switch, the screen goes blank again. Brightness isn't the problem, and the display itself clearly works fine.
Any idea what could be causing this? Is it simply the lack of keyboard, mouse, and software, or do I have to crack the case and replace some capacitors?