I have a 8x dvd burner. I used to burn dvd with speed of 8x. For some time now, my dvd burner only goes 4x. I used nero to test my dvd burner speed with a dvd+r and it only burns at 4x. The dvd can go up to 16x. Ever since i used any dvdr with 16x speed, it only goes 4x. I dont have any blank 8x dvdrs, only 16x. But when i tried using nero speed test to test the 8x dvdr i had, the speed said 2.49 or something. Also, when i burn a dvd either with nero or convertxtodvd, the burning takes about 30 minutes. The light on the dvd burner flashes on and off. It never used to do this. I tired unistalling the drivers but nothing happened.
Have you tried checking/enabling DMA?
It sounds like your drive firmware is not recognizing the media ID of the newer 16X discs.
We always need the drive, firmware, and media ID to do the best job on these problems. Please list this and we can most likely get you to the newer firmware, if available.