can you please post the hardware that you have installed?
not only vga card,motherboard, but everything inside out. SCSI hard drives (if you have), completely everything
and the version of red hat you .. purchased?
the first thing to check if there is some conflict with the hardware is to unplug everything and work only with the needed.
and then ofcourse install one by one to find out the one that has the problem
I'm not absolutely sure of the problem and I didnt't post a solution but a first step.
but again, post your hardware