I just received my Dell Dimension 8400 (Win XP) with the infamous Phillips DVD8631 last month. After going through what everyone else has to get it working... clearing LowerFilters, UpperFilters; downloading and installing firmware, clearing NVRAM, deleting and reinstalling software, removing drivers and rebooting, etc. etc.... it still wouldn't burn DVDs. It would burn CDs, and play CDs and DVDS... it just refused to burn DVDs.

 

Dell sent a tech to replace the drive. He spent two hours and couldn't make the replacement drive work. I contacted tech support again and again they scheduled a tech to come out and replace the drive. It was a nightmare.

 

Finally, I simply deleted Sonic completely from the the computer. I downloaded a trial version of Nero 6.6 and tried several different types of media including HP DVD+r 8x, Philips DVD plus+r 8x, and Memorex DVD+rw 4x. The Philips brand wouldn't work at all. The HP let me burn a disk, but it would play back. The Memorex worked fine. At Last! I went out this morning and bought some Memorex DVD+R 4x discs and they worked perfectly too. I've run several burns now and the drive is working properly.

 

If you're still having problems, make sure you have CD-21 firmware installed (check the Properties/Settings tab for the drive), get rid of Sonic and try Roxio or Nero (recent editions)... and try Memorex discs.  Good Luck!