are you running xorg or xfree?
hit ctrl alt backspace, do you get back out in cmd?
There has to be something with the x setup
try running xorgconf or check /etc/X11/xorg.conf or xf86.conf
xorg.conf or xf86.conf
monitor section, try setting the vert refresh and horizontal refresh rate as specified in your monitor specs, also try using another resolution, those can be commented or commented out in the screen section...
You just have to fail and try untill you get it right.
No two computer are the same
Post back if you still have problems..