After installing a new CPU cooling fan I experienced a problem with what was previously a working system.

I'm running a pair of 1800MP processors and 1 stick of 512 meg ECC registered memory in an ASUS A7M266D MB.

The issue is that the system will not post and gives beeps that the manual says means either the memory is not installed or not recognized.

To troubleshoot I installed both a single stick and then a pair of non ECC, non registered memory (appropriate type and speed) known to be good and still the same problem. The original 512 MB was removed for this test.

I installed the systems original memory (512 MB ECC registered Memory) into a different mother board and it would not recognize it but I'm not sure it could due to design. It is a Biostar M7VIG (VIA 266 chipset). I'm not quite sure how ECC registered memory works.

So my question is: based on the above description what is the likely problem, blown memory or motherboard? Is there anything else I should do to potentially fix the proplem?

ECC should work in other boards as long as they support DDR ram. Worst case you might've hit something or fried something installing the fan. Does your bios even boot up?