Did you buy a license for Red Hat? If yes, then you have paid for support. If not, I would highly recommend you find another distro. There are no updates to Red Hat without a license, and no support. Centos is a test branch of Red Hat, if you have to have a 'server' distro. Just understand you can add servers to any distro.
See this link -->
https://www.redhat.com/wapps/store/catalog.html
When the xserver fails to start, the first place to look is Xorg.0.log. There will be messages with (EE) in them. Those are the error messages you need to look at. Without more information, it is not possible to help any more.
Things to look at, do you have a propitiatory video card? ie Nvidia ?
Is the correct driver loaded for your video hardware?
Post the output of the command '/sbin/lspci | grep VGA' ( without the quotes ). That will tell us what video hardware you have.
Post any (EE) lines from the error log.
