Welcome to the forum
Does the drive work @ 8x? With good media that is, which brings me to my next question - what brand are the discs you're trying to burn?
Also, if you can download and run CD-DVD Speed, put a disc in the drive, and go to the "Disc Info" tab. Then post the MID info for the discs in question, that would help us to pinpoint the problem.
As it stands so far, it's looking like a dodgy media problem.