...what were you doing just before the drives went AWOL? Did you install new software, update Windows, anything? If so, then reversing those actions might bring the drives back.
Do the drives fail to show up in Device Manager at all?
Have you scanned your machine for viruses and other malware using fully updated programs?
Please do these things immediately and let us know what the results are.
Both my CD-ROM and my DVD R/RW have disappeared off my PC and are not working. Is there anything I can do to rectify this? My system is Windows 2000