Who ever changed over his mobo kept his adapter, thinking it wasn't needed anymore.
Yes, he should try the PATA on the PATA, with the jumper to cable select on the end (Master port) on the PATA cable. Same on his CD drive. He should post his motherboard brand and model number. It's hard to belove that he has one of those very few boards that had IDE and SATA that wouldn't allow BIOS select of which boot drive. That was the big selling point of those boards.... Adaptability.
I diagnosed this quick, but what should have worked on this was to mount the SATA (sdb, where his install is) and reinstall Grub with /dev/sdb/boot as the grub directory and /dev/sda (where his BIOS is locked into for the boot drive) to install the MBR.
Why that didn't work? Got me wondering.