Disappearing Hard Drive

Installed second hard drive, made it the boot drive and loaded XP and all app software on it. Made the old drive a slave drive and formatted it. The system recognized the old drive as :H and everthing was running great for over 2 months. Last week, the :H drive disappeared from the drive list, fortunately I hadn't loaded anything on it yet. Device Manager sees the physical drive but, XP and the app software does not see it. The old drive is a Western Digital and I've used WD's diagnostics but they don't see the drive either. I've reseated all the connectors on the drive, can feel the disk spinning, etc. Any ideas on how to get the drive back?

 

upgrade the firmware. search on google using the exact model number of your hdd.