Good job on figuring it out. Yeah... forgot that RAM is a possibility too. I should have remembered... a couple months ago, I had a system that had 4 x 2GB RAM in it, and now I recall I went through the exact same thing. It had worked perfectly fine for months, but then all of a sudden it wouldn't turn on anymore. Like I said, from previous experience, it had always been the motherboard for me in a case like this, so I went out and bought a replacement motherboard and swapped it... except that didn't work either. After that, I finally started testing the other components and discovered one of the four sticks of RAM was causing the problem. I find that very weird though because I had always thought that RAM was one of those components that either worked or it didn't, not something that goes bad over time.
But anyways... sorry for not remembering that to help you out, but good on you for figuring that out on your own.
