Replace the battery if you have not already. It will almost definatly fix the problem. In rare cases, you may actually have to replace the CMOS chip as it is possible that it has died. If you get a Rom burner, you can apply the lated update to a size matched chip and then just swap them out. The Error you are getting is due to an error in the code that is stored on the EEPROM chip. This will be cleared when the battery is removed. The EEPROM goes back to the factory loaded settings, and then can be upgraded to the newest BIOS revision.
The only other time you might see CRC errors is if you have a bad HDD or CD running. But since you are not getting past the POST, then your BIOS is the most likely culprit.
PS, one thing to make sure of, is that you have no power plugged into the system. Nothing at all. Remove the MOBO from the case and even take out the proc. Then remove the battery, and put a jumper on the power switch connector. This way, all of the power is released from the Caps on the Mobo and anything else that might hold some voltage. You have to Zero you board before the CMOS will be truly cleared.