Could be a simple case of a drive that has failed. Optical drives, burners in particular, fail pretty often. Anything over about a year of fairly regular use is just gravy.

It could also be that you've done something software wise, possibly even unintentionally, that is causing the problems.

A good test to see if it's hardware or software would be to download a Linux distribution you can boot off of a USB flash drive. Then try and burn a CD and DVD (both, since they use different lasers). If it works, you have a software problem, and if it fails, you need to replace the drive.