If the MoBo is replaced, you might just have to call MS and tell them to get a new key. Some folks, usually those that wink a lot (evil grin) would replace the MoBo and a whole lot more, but not disclose what else they have replaced. Lies? Not technically. Honest? Hell no! LOL
Linux is easy to install. Before xp, it was easier than windows. Sure, there is learning curve, but it comes with 1000's of apps pre-installed, including The GIMP, a Photoshop clone. Everything is different in Linux, so it is for the open minded. If you are a heard follower, forget it; if you have fun learning, you have nothing to loose but a blank DVD (assuming you can download an iso image). Also note, there are not many "gamer" type games. There are some simple amusements like xp comes with called games, but is not really a gaming OS.