Hard Drive not recognized with 2 drives

On a Gateway 700X, using Win XP Home, with a 80GB IDE hard drive, I installed a second 40GB IDE drive a few months back. Both drives are Western Digitals and all has been working fine until this week. Earlier I powered off the computer and then the next next powered on. The system wouldn’t boot. It wouldn’t recognize ANY drives. I tried swapping cables, re-seating, but nothing. However, if I just disconnect the second(slave) drive it boots fine. If I reconnect the second, again no drives are recognized. Any ideas appreaciated since this environment has been working for months until now.