Windows 7 Upgrade and CD/DVD ROMs

I recently installed a Windows 7 32-bit upgrade to XP on a Dell Dimension 4700.  The OS recognizes all devices (printer, scanner, sound, modem, hard drive, etc.) and they operate normally except for both CD/DVD ROM drives.   The OS tells me the device drivers are current but gives me a "Code 39" message.  Updating the drivers does not fix the problem and I cannot access either drive.  One drive came with the Dell PC (Hitachi 48x CD-RW/DVD) and the other was installed last year (an HP 1070i dvd writer).  Without working CD/DVD ROMs I cannot reinstall the old XP OS.  Suggestions?