I have a PC running Windows XP SP2, all the upgrades, too. Lately, the two CD drives don't show up, neither in My Computer, nor in the Belarc Advisor. It seems to be a little random, since one of them (AOPEN 1648 [X16 DVD/CD Reader, not burner]) shows up in the BIOS, and in the first boot-screen. The other one doesn't show at all. A week ago, I opened up the case, and re-plugged them. It helped, and I was able to use them until yesterday. Today, however, they dissappeared again. I tried opening the case, and checked the Master-Slave connection (They're both on the same cable). The middle one was Slave, the outer one was Master. I tried setting both to Cable Select, but it didn't help.
Both drives work (were tested on other systems), on the same cable.