I'd say that the first thing that you should do is to look at the X logs in /var/log. It's quite possible that the casue of the error will be listed in there. I'm not on a Linux machine right now, so I can't remember their exact name, but it should be fairly obvious which ones they are.
The Linux logs are the best place to start when troubleshooting any problem.
The information on Computing.Net is the opinions of its users. Such
opinions may not be accurate and they are to be used at your own risk.
Computing.Net cannot verify the validity of the statements made on this
site. Computing.Net and Compnet Ventures, LLC hereby disclaim all responsibility
and liability for the content of Computing.Net and its accuracy.