I have 5 hard disks built in my computer, two connected by IDE cables, three by SATA. Today I had to return two of the SATA cables to my room mate. So I grabbed another one I had floating around and connected the remaining disk by unplugging my DVD R/W. Now I receive the 'insert system disk and press enter' error after booting. Disks and cables seem to be fine, since all the disks are recognized in the BIOS. Also, I can mount the disks using a live CD w/o problems. I also tried different orderings of the cables (i.e. plugging the disks in different plugs on the mainboard), I'm not sure if that even matters using SATA. Any Ideas what might be the problem here? The OS installed are Windows 7 and Ubuntu 10, the bootloader installed is GRUB.

PS: No RAID involved, JBOD.