Did you set one as master and one as slave? Then plug them both into the same IDE cable. I don't remember if the master or the slave has to be on the connecter on the cable that's closest to the motherboard. Make sure the cables aren't hooked in the HDs upside down, sometimes you can jam it in the wrong way. Maybe sure power cables are plugged into both HDs. I only mention all these things because they're things I've forgotten to do myself. Does it boot to the BIOS when both are plugged in? If so go check IDE configuration in there, it'll show which drives it's recognizing and which it isn't, so maybe that'll help you figure out where the problem is. Maybe try booting with just the second HD, to make sure the drive isn't destroyed or something. My strategy is usually to randomly plug things in and flip jumpers until something works, so I'm not the best person to give advice I guess.