Firstly, I'm not sure what you mean by 'everything loads fine' if your not getting any output on the screen or any beep. Just it just sit there with the fans running or what? Can you clarify?
I can only give general advice as I've never used the exact hardware you have but I had a quick look at the manual on the Asus website. I would:
- double check that the correct number of stand offs (the things you screw the board into) are fitted to the motherboard tray and are in the correct place. Any unused standoffs can short something out on the back of the board and cause problems.
- work through methodically, checking that all of the connections that should be there are. For example the 24 pin ATX power connector is probably connected as it's the obvious one, but is the 8 pin (EATX12V) power connector, and the graphics card power connector(s) etc? Work through each step of the manual Chapter 2.
- if using multiple memory modules, try booting with just one of them installed. Maybe try different memory slots.
- to clear the CMOS you unplug the computer and move the jumper cap from 1-2 to 2-3 for 10 seconds or so on the CLRTC jumper (manual page 2-15)
- read manual page 2-16 with regard to the "Mem OK" switch. Are you getting the LED lighting continuously? If so try as suggested in the manual.
The optical drive you'd need would be a SATA one, which uses the thinner SATA cables. This is the standard now, the old IDE drives are slowly becoming less common.
EDIT
To try to rule out the video card as the culprit, do you have an old one you could try? The case is unlikely to be a problem, but the issue of having some piece of metal (like an unused standoff) shorting out the back of the mobo is one that has caught me out in the past.
Regarding the power connectors, just make double sure that the 4/8 pin EATX12V connector on the mobo is connected to the right connectors from the PSU. This 12v connector directly powers the CPU, and with some power supplies, it's not always totally obvious what wires need to connect to it. Sometimes you have two 4 pin plugs that lock together to make the 8 pin connector, The symptoms where the CPU power connector has not been connected is normally the system turns on, the fans spin up, but it doesn't do much else and won't turn off again without holding down the power switch for 5 seconds,
If it's all been put together correctly, everything checked, troubleshooting procedures followed, then the only thing you can really do then is start swapping out parts for known good ones until you find the problem.