Hi
I can't offer much help, but I've had this happen to me with RH 6.1 (fixed when I upgraded to 7.0 - which isn't of great help to you)
Anywho, try re-installing (bummer I know) but use FDisk on the RH partitions instead of simply writing over them, as they can still be corrupt if u install a slightly different (or even similar) configuration ontop.
Then make sure you choose a very low level resolution and color bit level (i.e. - 640x400 & 8bit)
The hopefully it should boot up X and once your in, run Xconfigurator as root, and change the res, and bit levels to what you want.
Worked for me, but good luck!
let me know how it goes
JoE