I had a P4 1.4 GHz system flawlessly running with 2x128MB Non-ECC 400MHz RAMBUS Kingston Value RAM. Motherboard ABIT TH7-RAID.
Recently I bought 2x512MB PC800 ECC HP RAM.
I could not make my system boot with this RAM and frequently it would not pass the POST test stopping on 'C0' (Memory detection). I tried as many configurations as I could with 4 slots and the old and new memory in pairs and also used my continuity RIMMs. Any configurations with new RAM would not boot. I managed to get the system to just about boot by clearing the BIO's using the motherboard jumper but the system still seemed unstable and the processor/memory were running at very low default speeds.
Removed new RAM and system is again fine.
Seller assures me that he tested the memory and its ok. Is it duff memory? Incompatible motherboard? Or will a slower RAS/CAS figure maybe help?