I think that the thing to do is to remove everything bar the RAM and graphics card, thats HDD, sound card etc, and try and turn it on. If the mobo is ok it should still go through the POST checks and tell you that it can't find a system disc. This will tell you that the mobo is ok so the problem is elsewhere. Then add components one at a time booting up each time until it fails, this will tell you which bit of hardware is knackered. If it won't boot in the first place and you have 2 sticks of RAM, try it with just one, then swap to the other stick if that doesn't work. The green light on the mobo suggests that the power supply is ok.