Weird Mobo Problem...

I just bought a Shuttle MOBO w/ Athlon 2700+ combo. The problem is that 90% of
the time when I hit the power button, the CPU fan and the MOBO power light up,
but I don't even get a post from the mobo. It does this even when I only have
the video card hooked up. 10% of the time it does post and boot up normally,
but it erases the FSB memory in the BIOS setting, and boots up at 100 Mhz FSB
setting. However, if I get into BIOS, it go back to 166 Mhz on reboot even if
I don't do anything and just exit. Anyone knows what is causing this? I've
exchanged the MOBO and power supply from the place I bought this at, and I
switched out the memory, but it still does this...I'm totally stumped...

Grativo