Um you can adjust the burning speed in nero if you put your CD-R in before you click on write. I have this problem too. When there's no disc in the drive it just says "MAXIMUM" for speed setting and either doesn't let you change it or only lets you change it to 2 different speeds which normally I wouldn't want either.
What else to suggest? I have no idea man... if I don't use nero, I actually create the ISO in nero then burn it in alcohol 120%. Nero and alcohol work fine. If all else fails, buy a new burner and try again.