you've probably blown the internal fuse. look at the top left of the board, see that gap with a black thing bridging it? it's a 1.5 amp picofuse. if you've got a continuity tester then you can test it
i couldn't find a direct replacement, so used a 1 amp picofuse instead. some people use just a bit of wire to replace it, although it's probably not very safe.
next time, after you unplug you snes, switch it on before taking it apart, you'll notice the power led flashes - this dishcarges any electricity.