Philips DVD8421 Problem

I have a Philips DVD8421 (at least that is what it says it is). Until a few weeks ago I could make my own movies using either Nero or InterVideo, then I started getting a slight pause every few seconds on the finished DVD.

I tried to resolve this by using different DVDs, defragging my hard drive, shutting down other programs whilst buring. In the end I resorted to downloading some firmware recommended by HP (9H10), previously I had 6H01 firmware.

Unfortunately, my drive now only recognises CDs and not DVDs. In the Hardware Devices it is listed as a CD Drive. Any ideas how I can get it back to recognising DVDs or do I have to buy a new DVD Burner?

Any help would be gratefully received, as I am out of my depth !