I recently built my new system, Asus P5N-E motherboard, Q6600 processor, 4Gb RAM, 8600GTS video card and 500Gig Samsung SATA HD.
After the usual teething problems, it is now stable and boots every time. However, I am now getting the 'CMOS Checksum Error - Defaults restored' message when it is a cold restart. I thought that it must be the CMOS battery, so I replaced it, but the problem has not gone away.
If I just shut down the PC and don't remove the power, then it will restart every time without the CMOS error. This also seems to suggest that the battery is the issue On the positive side, it seems to suggest that the CMOS chip itself isn't the problem.