I suppose yours is installed with Vista?
I would attempt a repair with the recovery disc first if you have one.
If it doesn't work, here is a method that's mentioned on a lot of times on different websites and seemed to have worked for some people. But proceed with care and at your own risk because it involves registry edit. Have everything backed up.
A week agao, I was silly enough to try a Blue-ray disc with my DVD drives. The Lite-on didn't like it and immediately had it ejected. The Pioneer didn't like it either but refused to return it. I tried various methods, soft (eject, reboot) and hard (a pin) but the Pioneer just went to sleep. I couldn't see it in My Computer any more. The problem was finally fixed by having the DVD drive "reseated". I unplugged the SATA cable, plugged it into another socket on the motherboard and then reboot. I don't know how to do it with a laptop.
Australia, home forever.