I'm trying to build a computer (for the first time).
My motherboard is a Foxconn A7GM-S.
When I turn it on, it doesn't post. The power LED, all fans, optical drives, and hard drives seem to work, but there's no video signal. I tried both the onboard video port and my graphics card. I tried removing all drives, 1 stick of RAM (leaving 1 in), all PCI[-E] cards, and it still doesn't post. After checking the motherboard manual again, I found out the diagram for the 24-pin power connector was upside-down. So I guess the question is: What's been fried?
Try removing the motherboard from the case, sit it on its anti-static bag and use only the essentials (ie: cpu w/ heatsink & fan and one stick of ram, nothing else not even hard drive). Plug in the appropriate power cables and video cable. See if you can get it to post like that. If it doesn't post then the motherboard may be dead.
EDIT: Excellent point by Colegade, there's always the possibility that the board doesn't like your ram, but in that case you should at least get the board trying to power up but beeping or otherwise notifying you that it's not seeing the ram.
Are you sure the RAM is compatible with that particular board? I've had a few situations were a few Gigabyte boards refused to post with some DDR2-800, and DDR2-667 from G. Skill. Went out and bought some Corsair DDR2-800, and it booted right up.
Make sure the CPU is seated correctly, and if you happen to have some other RAM you could test out with it, I might try it. But otherwise If your sure the CPU is seated right, and that the RAM should be compatible. Last resort is too take it out of the case and place it on a box, and try to boot it up there. (To eliminate the chances of a short occuring)
Are you using stand offs between the board and your case?
Be sure you have a working speaker connected to the MB speaker header. Remove all the RAM and boot the system. If the BIOS does not beep indicating no RAM in the system, you have a bad MB or CPU. With your new buld, provided the CPU is supported by the BIOS version you are using.