Computer not booting

Hi folks,

I have a shuttle SG31G2 (you can see the full specs on their website or on newegg's website). I bought it from newegg. I installed an Intel Q6600, 2 x 2Gb of G-Skill F2-6400CL5D-4GBPQ memory, a Lite-On lightscribe DVD burner and a HITACHI Deskstar 500 GB hard drive.

However it boots sometimes and sometimes it won't. I tried other memory modules like the OCZ Vista Upgrade 4GB (2 x 2GB) 240-Pin DDR2 and some Corsair 1GB 240-Pin DDR2 sticks as well. Those did not fix the problem. The computer will not boot. I got it to boot by taking out one of the memory sticks and resetting the CMOS.

And when I do get it to boot, the processor is underclocked at 1.5 Ghz instead of 2.4 Ghz. If I go into bios and try to change anything in the bios, the system will not boot. Even if I go into bios and don't change anything, the system will not boot again after I exit bios. I have to reset the CMOS again in order for it to boot.

Do you have any ideas? I'm tired of buying memory sticks that don't solve the problem. Could it be the motherboard? The only thing that I have not swapped out is the processor because I've been told that those usually are the last place to check. Please help, this can be a very sweet system if it's working correctly.