|Are you sure this a BIOS ROM Checksum Error or a CMOS Checksum Error. There is a difference|
The former is extremely rare and difficult to fix the latter very common and easy to fix. The CMOS Checksum error is fixed as described above
A BIOS Checksum error indicates that the BIOS has become corrupted and as such, it cannot do anything. As the BIOS is in ROM it is very difficult for it to get corrupted but that can happen, especially after flashing the BIOS.
So did you flash the BIOS recently?