Open up your Device Driver list and see if the driver has become corrupted or missing.

You might need to download an update; or if an update has spoiled the function of your drive you might need to roll back to an earlier version.

The registry might be corrupted. If updating the drivers does not work, you may have to reinstall Windows or try Regclean or some other form of registry repairing software. Registry repair can damage the operating system so be careful.

This is a safer avenue to explore first, before attempting registry repairs or OS reinstalls: Possibly there is some piece of software, resident in memory, stopping you playing DVDs, so you may want to uninstall and/or reinstall any DVD playing software you recently installed, or find a new one and and install that.

It actually might be that the codecs are corrupt and not the drivers for the dvd drive.

Download VLC and see if that will play the DVD. The program should play damn near anything.

A lot of the DIVX players will also play DVD's so you might want to try one of them also.

If he cannot burn DVD's, then it probably is not a codec problem, but it is another possible solution after every other easy solution is tried. It depends on the program he is using to burn and the DVD type he is making. Try making a data DVD with some random files from the hard drive, and if that works, then it might be a codec issue, if making a video DVD still fails. Again it depends on the program used to burn also.