Solution : Light up display & Enable GUI
Edit xorg.conf file
Login as root and Backup xorg.conf using the following command
#cp /etc/X11/xorg.conf xorg.conf.bak
Edit xorg.conf file
#vi /etc/X11/xorg.conf
Duplicate the following in xorg.conf
Section "Device"
Identifier "ATI Technologies, Inc. 3D Rage Pro 215GP"
Driver "ati"
BusID "PCI:0:18:0″
Option "UseFBDev" "true"
EndSectionSection "Monitor"
Identifier "iMac"
Option "DPMS"
HorizSync 58-62
VertRefresh 35-117
EndSectionSection "Screen"
Identifier "Default Screen"
Device "ATI Technologies, Inc. 3D Rage Pro 215GP"
Monitor "iMac"
DefaultDepth 16SubSection "Display"
Depth 1
Modes "1024×768″ "800×600″ "640×480″
EndSubSectionSubSection "Display"
Depth 4
Modes "1024×768″ "800×600″ "640×480″
EndSubSectionSubSection "Display"
Depth 8
Modes "1024×768″ "800×600″ "640×480″
EndSubSectionSubSection "Display"
Depth 15
Modes "1024×768″ "800×600″ "640×480″
EndSubSectionSubSection "Display"
Depth 16
Modes "1024×768″ "800×600″ "640×480″
EndSubSectionSubSection "Display"
Depth 24
Modes "1024×768″ "800×600″ "640×480″
EndSubSectionEndSection
Save and exit the file
Restart the Gnome Display Manager (gdm) using the following command
# /etc/init.d/gdm restart
Boot into the X Windows System (to let you login, use Debian with a GUI) Type
#startx
