What version of RedHat?
The most common cause of this is a missing video driver. Please tell us what your hardware is (including what video card), and then run dmesg to see if you can find evidence of the card.
Example (my system)
lspci finds this:
01:00.0 VGA compatible controller: nVidia Corporation Quadro FX 570M (rev a1)
Then I do: "dmesg|grep -i nvidia" and get this:
nvidia: module license 'NVIDIA' taints kernel.
nvidia 0000:01:00.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
nvidia 0000:01:00.0: setting latency timer to 64
NVRM: loading NVIDIA UNIX x86_64 Kernel Module 190.53 Wed Dec 9 15:29:46 PST 2009
Among other things, this tells me that the video driver is working.
You can also look at /var/log/Xorg.0.log for clues