First, right-click My Computer, select properties, select the hardware tab, and click Device Manager. From there expand DVD/CD-ROM drives and see if there are any alert icons shown. If so it's a driver issue that can be easily solved...just report back the drive's model number (it should be the name of the device in Device Manager but can also be determined by using the free program Everest) and we'll direct you to the proper download.

Next, check that the cables are still firmly connected, especially if you have recently moved or worked on the computer. Just open up the case and make sure that the power cable is plugged into the CD-ROM drive, and the the IDE cable connection is secure in the drive and motherboard.

Finally, try replacing the drive as it's likely passed on. Two years does seem a little early for it to die, but it's not uncommon, especially when companies use the cheapest parts possible to keep their own costs low.

Hope this helps,
John