Dontcha just hate those mysterious problems? lol It could be a multitude of things.
Have you checked fuses and electrical connections to make sure you have a good contact and no high resistances? It could be that there's a loose fuse, maybe a relay fuse. When the car won't start, do your power windows work or are they buggered out too?
Can you hear the fuel pump when you power everything up? Check for any overheating, or the obvious fluid levels?
There are so many possiblities, I've seen a similar problem on a few cars now, and one truned out to be a loose fuse (that was my own car), one turned out to have some corroded wires sending mixed up signals to the ECM, and another one wasn't electrical, and I didn't get to hear the diagnosis cause buddy sold the car instead of trying to fix it
