Help tsh552b started burning slow



hey, I got the samsung tsh552b, use nero6, have been using the same media
memorex, for about 3 months and all of a sudden, at 6x it is taking over 1/2 hour to burn a dvd…
it may have started after I tried to burn a video CD… if I changed any settings I don’t remember… as you can tell, I am new at this, any help would be appreciated