CD/DVD not working -error code 39

My CD/DVD drive is not working. It is recognised by the computer and it lights up when I put a CD/DVD in, but It doesn't show up in "My Computer". In Device Manager it says "Windows cannot load the device driver for this hardware. The driver may be corrupted or missing. (code 39). I found something called " firmware" on Dell web site for my model, but not sure if that means "driver". The number is slightly different.

HLDSGSA-H21N-HH-16XDVD+-RW PATA instead of
HL-DT STDVD+-RW GSA H21N which comes up in Device Manager.

Also, this is not the original DVD drive as the first one broke and was replaced (on site) under the warranty with a different one. I do have a few software discs that came with it but of course the computer isn't reading the disk drive. I also checked the BIOS and it appears to be recognised there also on Drive 2 PATA - 0.

Purchased computer in 2006 so of course is now out of warranty.
DELL Dimension E510 - Model DM051 -Windows XP Home Edition with all the updates.

I have tried unistalling, rebooting and reinstalling the drive but it hasn't worked.

Sorry to be so wordy but I just don't know what to do.

How can I find the right driver?   Hope someone can help.

Thanks in advance.