DVD Burn Errors

I am using nero on winxp sp2. I have a plextor px-712a drive. Ok so i have been using this drive for about 6 months with no problems. Now the last three time i have tried to burn a dvd i get dvd failed at 8x. Why would the burning just begin to fail after so may successful burns? Also, it use to take about 8-10 min to burn a disc now it takes 30-45 mins. Any suggestions? thanks!

try different media. slower speed. make sure DMA is enabled