Computer will not Post, But powers.?

well it sounds like the power supply. but they may not be it if you say it works some of the time. and if its the ram, take the ram out and try and boot it. even without the ram sticks you should still make it to the bios with the on board ram alone. oh and disconnect the hard drive to. in fact disconnect anything you dont need to get to the bios. doing this might help you figure out what is holding you back. but it would help alot more if i new what you're computer spec's were