[ASRock] 775Dual Bios / CMOS Bad Checksum error - not battery related

I recently flashed my ASRock 775DualVSTA mobo with a modified BIOS, and now when I boot my PC I get a CMOS Bad Checksum error.

I did some Googling which resulted in me clearing the CMOS for about 15 mins, then bought a new CMOS battery. Neither of these things worked.

When I boot, and I get the CMOS error, I have two options:

1. F1 option of continuing with default settings. When I do this, I get a "NTLDR missing" error which I think is because my Vista is installed on my SATA HD and my BIOS won't recognize this drive as I haven't enabled it in my BIOS (as it's running to the default settings).

2. F2 option of going into my BIOS settings. Doing this, I want to get my BIOS to recognize my SATA drive with my Vista install. By default the BIOS sets the SATA option to RAID and I don't have a RAID setup. So, I switch it to non-RAID, save changes, and reboot. However, just after the POST, I get the same CMOS bad checksum error, meaning I'm back to square one, and a vicious circle.

I wanted to reflash my BIOS, so I created a bootable USB drive with basic DOS and my flash program, but I can't get it to boot from my USB as I think it's looking for my SATA HD, which goes back to the "NTLDR missing" error.

I also looked into getting a bootable CD working, but again I get the "NTLDR missing" error.

Does anyone have any suggestions on how I can get my BIOS reflashed?

Do you think that my BIOS is messed up?