When you first boot up, is either or both seen by the BIOS. If not, suspect either the cable or the IDE channel. Check all connectors, both power and IDE on both and make sure you have no bent or broken pins. Next, see what happens if you only have one as the master. One or other of the drives (I don't believe in coincidences but it COULD be both) could have failed.
Next try attaching one as slave to HD and see if its seen. If this brings it to life, it will indicate a mobo problem.