Comment 39 for bug 224404

I also had the same problem with a Dell Optiplex 755 with a Radeon HD 2400 Pro when using 4gb of memory on an amd64 (x86_64) install of RHEL5.2. Disabling mtrr in the xorg.conf and disabling redhat's graphical boot seemed to do the trick. I'd like the pretty graphics on boot so users aren't exposed to that, but I can live without it. So my changes in sudo diff format:

/etc/sysconfig/init:
- GRAPHICAL=yes
+ GRAPHICAL=no

/etc/X11/xorg.conf:
Section "Device"
- Option "mtrr" "off" # This would use fglrx's own mtrr mapper code
+ Option "mtrr" "on" # Instead let the system handle it
    Option "no_accel" "no" # but keep accelleration
    Option "no_dri" "no" #and dri
EndSection