I had the same problem. There are a few services that will replace the power button for you. A site called mobiletechvideos.com used to do it for about $30. If you're handy with a soldering iron, you could try replacing it yourself. Let me warn you, though: speaking from experience, the Infuse's motherboard has some tiny connection pads. It's a painful repair.
Another idea I had, back when mine went kaputske, was to buy a broken Infuse from eBay, and cannibalizing it for the motherboard. But with that route, you usually have no idea if the mobo works, or if the power button has the same issue.