As dionb mentioned, the typical show-stopper (often mis-attributed to ECC) is whether the module is Registered or Unbuffered. Those cannot be mixed and they have to match what the board requires. However, it looks like that's not the problem here. I found the same as cyclone3d that these are apparently Unbuffered ECC, not Registered.
It's a longshot, but try resetting the CMOS settings before attempting to boot with this RAM. Maybe there's something stored in the settings that's keeping this RAM from working.
It's odd that it's not beeping. Normally if there was a RAM issue most BIOSes would beep at you.
The only desktop (expecting unbuffered memory) motherboards I've encountered that would refuse to boot with unbuffered ECC memory modules were DDR1 Dells like the GX260 and GX270, etc.
In the DDR1 and SDRAM era, every non-Dell motherboard I've used has been indifferent to the extra 8 bits of bus width provided by an ECC module. Those bits just go unused and the memory works fine.
Unbuffered ECC is fairly common pre-DDR2, but I suppose by the time of DDR2 maybe it wasn't common anymore, and maybe desktop boards in the DDR2 era might have developed a Dell-like attitude problem against running it.
I don't know, I've never used anything ECC in the DDR2 era or later. All my ECC stuff is DDR1 or PC100/133.
