No Boot: Shuttle MV43VN, P4 2.4 w/ 1MB & 533MHz, 512MB DDR266

I'm building a system for my biz, and it's having trouble booting.
That is, there is no boot - all fans spin, but no POST display, HD
doesn't seem to spin up, CD drive doesn't even open. I've swapped-in
an identical motherboard, CPU, memory, a 40GB hard drive, and it still
has a boot problem. I even tried a different case w/ different power
supply, to no avail.

My main suspect is the 1MB cache on the processor, because that's the
only thing different from my normal system builds (got a deal on some
1MB P4's). The weird thing is that it *has* worked sometimes - booted
up several times, to the point that I got Win XP and some drivers
loaded. But from the start it hasn't been starting every time, and
now it seems to be completely dead to the world, with the exception of
the spinning fans. Does anyone have any ideas as to what could be
causing the problem? Is there some special motherboard spec to allow
it to accept a 1MB cache P4 chip?

System setup:
Shuttle MV43VN mATX motherboard
P4 2.4GHz w/ 533MHz & 1MB cache
512MB DDR266 SDRAM
WD1200JB hard drive by Western Digital
Sony 52x CD-ROM drive
Codegen case w/ 350W power supply

Any help would be appreciated!

Thanks,
PeteCz