1st of all
Do you got a login screen?
(also a prompt on a black screen would be nice)
2nd In case 1st is answered with yes
and you're able to login as root
and go on to step 3
3rd check your /etc/inittab
- at the point default runlevel 3 would be no GUI and 5 would be with X
4th if you see that in step 3 you have got inittab checked change 3 to 5 otherwise
if step 2 the runlevel determine thing said 3 then just enter init 5
if still no login in screen check
cat /var/log/X.org.log for any errors
or just enter
as step 5.
Post your errors and outputs and so on here