Spilled soap on the motherboard, how to clean?

distilled water on a lint free cloth and let it dry totally before you switch it on.

other than that get some electronic component cleaner and clean it gently. While your at the shop get a antistatic wrist strap and use one of these first. they are not very expensive and always come in handy.

Rubbing alcohol.

http://www.badcaps.net/forum/showthread.php?t=1463

CRC QD Electronics Cleaner, [Can be acquired from any auto parts store] is probably the best thing on the planet to remove all traces of water and any deposits left behind by additives such as Water Wetter, which was what I was using at the time that exact same thing happened to me.

CRC also makes an electric cleaner, the QD Electronics Cleaner will not damage any substrates or plastics, on the graphics card or M/B, I had crud in my PCI-E slot that had to be cleaned out and the QD cleaned it to brand new in seconds.