Oh no, that's a bummer about your Thumby! Water damage can be tricky. Since the rest seems to work, it might just be corrosion on the power switch contacts. Maybe try very carefully cleaning around the switch with a tiny bit of isopropyl alcohol (90% or higher) and a cotton swab. In the meantime, if you need a quick distraction while troubleshooting, have you ever tried Snow Rider 3D on a phone or computer? It's a simple but surprisingly addictive game. Hope you get your Thumby fixed!