DVD Writer not working. I hv a Lenovo laptop with Win XP SP2. It has got a DVD writer in it &

Question

I hv a Lenovo laptop with Win XP SP2. It has got a DVD writer in it & i use Nero 7 for CD/DVD burning purposes. The problem is whenever i want to burn a DVD now, it gives an "Power Callibration error" & my DVD is ejected. What's the problem??? Whereas few weeks ago it was working perfectly fine. Plzzzz help....