A checksum error means that there is a problem with the BIOS. This is different from the CMOS. The BIOS is in a flash rom and is the code that you change when you flash your BIOS. The CMOS is in volatile memory that is maintained by the battery, and only contains the settings for the BIOS and clock. If you are getting checksum errors, this suggests to me that there is a problem with the BIOS chip. Flashing the BIOS may correct this. My ASUS A7V8X-X motherboard has the facility to boot from a floppy if the BIOS becomes corrupt, and this may be the message that you are getting. This floppy is completely different from the Windows boot floppy.