The first thing I would try, uninstall/reinstall Nero, IF you know that your system is functioning normally in other respects. If after reinstallation the situation remains static, I'd be looking at erratic hardware function and would look into replacing the optical drive.
I've used Nero 7 Premium For Years Now To Convert My .avi and .mp4 movies to mpeg2 and dvd then burn to a disc. It has always taken between 1.5-2 hours. This week it suddenly started taking 6 hours to do and the last 20 minutes of the DVDs skips and freezes. What could have happened?

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