I installed centos 6.3 Final . But after rebooting it stuck and doesn't show GUI
I guess you need to start X-Windows manually.
Configuring to make it run automatically:
I just had the same issue, but in my case it was too little RAM. (On about the 10th install attempt I saw a message flash up very briefly stating this).
It seems that if you have too little RAM or video memory it defaults to a text mode installer and does not install X.
1GB was enough (started with 512MB)
Dear I also did this right after @Spackot reply but in vain.
It gave me some repositories error although I was connected to internet but still it happened.So i simply reinstalled centos.
But this time I checked the video memory settings. And there were only 1MB memory assigned by default so I assigned 70MB and also selected 3rd option while Booting. Which is Install OS which Basic Video drivers and it worked.