I was installing Ubuntu on a computer on which Windows XP was already installed. The computer has multiple hard drive bays, so I decided to remove the XP HDD and install Ubuntu on a blank HDD when it was the only HDD in the system. Unfortunately, if I now try to boot Ubuntu with the Windows XP drive in the second slot, nothing will boot. However, if Windows XP is in the first slot, it will boot fine.

Can anybody explain why this happens? When I was checking out the BIOS to see if something was messed up, I discovered that when Ubuntu is in the first slot, the BIOS doesn't recognize any HDDs. However, if XP is in the first slot, the BIOS recognizes both drives. Any hypotheses about why this happens?

Edit: Here's the setup. I have an old server with seven SCSI HDD slots. I have five identical 68 Gb SCSI drives, but I can keep only two plugged in. XP is still installed on the first drive, but I reinstalled Ubuntu on the second drive and had Grub overwrite the XP bootloader on the first drive. Now, the setup works fine, and I can use Grub to load either XP or Ubuntu.

However, if I plug in another identical blank HDD in the third slot, the computer recognizes only the XP drive and doesn't boot. Grub starts to load, then gives me a "disk not found" error. Running ls from the grub rescue prompt only shows one drive with two partitions.

I guess this is a BIOS problem, but I'd still like to know what triggers it. What about a blank drive could cause the BIOS to freak out?