You take things far to intense and to literal. First for either Gnome or KDE to be installed and working a version of X-windows is required. This means Xfree86 or newer, CentOS has/had
a newer version from xorg.org installed.
Get the list of your currently installed xorg.org rpm packages and reinstall them, place all that you need to reinstall in one common loaction where they are only rpm packages then as root do something like;
rpm -uvh xorg*.rpm --force
I'll leave up to you learn how to boot into runlevel 3 (hint rtfm).
No, just kidding....... When the grub splash screen is displayed press and key. Select the Linux boot choice and press the 'e' key. Select the kernel line and press the 'e' key again. At the end of the line add a space and the number three (3). When done press the 'Enter' key followed by the 'b' key, log on as root and supply root's password when done.
Second CentOS comes with vnc (the client) and vnc-server install/use them.
yum -c 'install vnc vnc-server'
For how to configure, please read: http://fedoranews.org/tchung/vnc/