K8M Neo-V won't boot from hard drive after BIOS flash

But it boots just fine from CD or floppy.

I bought the combo (MB, AMD64 processor, 1G memory) to replace a
motherboard which had died in a previously working system. At the
same time I replaced the power supply and the video card. When I first
fired it up, it brought up the boot manager from the previous incarnation
of the system, which had been an Athlon-XP.

I never actually let it reboot, since I wanted to redo the OS optimized
for the AMD64 (and the new video card.) I flashed the motherboard to the
most current version of the BIOS (AMI version 3.5), booted from CD and
installed the OS. Once I got to the point of being able to boot from the
new system, I removed the CD and proceeded to reboot.

It displayed all the possible boot devices (note that the floppy and CD
were empty):
Searching for Boot Record from floppy..not found
Searching for Boot Record from CD/DVD..not found
Searching for Boot Record from IDE-0..not found

No matter what I did, I couldn't get the system to boot from the hard
drive. I reflashed the BIOS back to 3.2, still didn't work. Since then I
have installed four different operating systems: Win2k, WinXP, Gentoo
Linux and Debian Linux. All boot from CD, install perfectly until you get
to the part where the system has to boot on its own, and then nothing.

Has anyone seen this? Is it possible that there is a problem with how
I've set the BIOS up? Or a hardware conflict with something else? Or
just a bad MB?

Thanks for any advice.
Steve