H:\is not accessible

I have an HP Pavillion A1710n running XP with three hard drives, all Seagate. I had the operating system and program files on the C drive and all my files on the D drive. The third drive was a backup. I had the backup sceduled weekly to backup My Documents from the C drive and all of the D drive. Once before after the backup ran I got an error "D:\ is not accessible file or directory is corrupted and unreadable". This wasn't a big issue I reformatted the D drive and restored the files from the backup. This time the I got the same message but for some reason the backup only copied My Documents none of the D drive files are there. I tried taking the D drive out of my computer and putting it into my wife's but all it did was rename the drive H and I get the same message when I try to access it. Under Properties of the "H" drive it shows capacity as 0 bytes. I haven't done a CD Backup in several months so there a lot of files on that drive that I would really like to recover. Any suggestions would be greatly appreciated

.Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows XP Home Edition, Service Pack 3, 32 bit
Processor: Intel(R) Pentium(R) 4 CPU 2.80GHz, x86 Family 15 Model 3 Stepping 4
Processor Count: 2
RAM: 2559 Mb
Graphics Card: NVIDIA GeForce 8400 GS, 512 Mb
Hard Drives: C: Total - 71332 MB, Free - 25642 MB; D: Total - 4966 MB, Free - 1024 MB;
Motherboard: ASUSTeK Computer INC., Grouper
Antivirus: Microsoft Security Essentials, Updated: Yes, On-Demand Scanner: Enabled

This is the info on ny wife's computer which is the one the harddrive is in now. As you can see the "H" drive doesn't even show up but it does show up in My Computer.