Wont boot from harddrive

Hi, I recently installed a new DVD-RW drive and my computer wont boot from the harddrive when the IDE cable is attached to the dvd drive. Both the harddrive and the dvd is recognised in BIOS. I set the boot priority to boot from hard drive first, but when ever I try to boot the system hangs for a couple of seconds, then it says “boot from CD…” Any idea why this may be happening? Both devices are on the same IDE cable.