Yeah, make sure that the positive and negative pins are on the right way around. That goes for all the switch connectors.
A system not posting certainly means that it's a hardware fault. Since you've eliminated the graphics card, it will be either the CPU, RAM or the motherboard itself. If all your switches (power, reset), etc are wired correctly and the problem with them still persists, then I'd put my money on it being a faulty motherboard.
TMT.