LinuxQuestions.org - X server working only at 640x480 resolution

Hello,
I have installed Fedora Core 1 on a DELL Optiplex 170L machine in which the monitor is replaced with older Dell monitor. This monitor is able to give 800x600@85Hz and 1024x768@60Hz under windows. In linux, I am not able to get resolution higher then 640x480. The monitor is detected as Dell E551a monitor. Please suggest modifications in configuration that will allow me at least 800x600. Attached is X Server configuration file.

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[root@localhost root]# uname -a
Linux localhost.localdomain 2.4.22-1.2115.nptl #1 Wed Oct 29 15:42:51 EST 2003 i686 i686 i386 GNU/Linux
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XF86Config File:
# XFree86 4 configuration created by redhat-config-xfree86

Section "ServerLayout"
Identifier "single head configuration"
Screen 0 "Screen0" 0 0
InputDevice "Mouse0" "CorePointer"
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "DevInputMice" "AlwaysCore"
EndSection

Section "Files"

# RgbPath is the location of the RGB database. Note, this is the name of the
# file minus the extension (like ".txt" or ".db"). There is normally
# no need to change the default.
# Multiple FontPath entries are allowed (they are concatenated together)
# By default, Red Hat 6.0 and later now use a font server independent of
# the X server to render fonts.
RgbPath "/usr/X11R6/lib/X11/rgb"
FontPath "unix/:7100"
EndSection

Section "Module"
Load "dbe"
Load "extmod"
# Load "fbdevhw"
Load "glx"
# Load "record"
Load "freetype"
Load "type1"
EndSection

Section "InputDevice"

# Specify which keyboard LEDs can be user-controlled (eg, with xset(1))
# Option "Xleds" "1 2 3"
# To disable the XKEYBOARD extension, uncomment XkbDisable.
# Option "XkbDisable"
# To customise the XKB settings to suit your keyboard, modify the
# lines below (which are the defaults). For example, for a non-U.S.
# keyboard, you will probably want to use:
# Option "XkbModel" "pc102"
# If you have a US Microsoft Natural keyboard, you can use:
# Option "XkbModel" "microsoft"
#
# Then to change the language, change the Layout setting.
# For example, a german layout can be obtained with:
# Option "XkbLayout" "de"
# or:
# Option "XkbLayout" "de"
# Option "XkbVariant" "nodeadkeys"
#
# If you'd like to switch the positions of your capslock and
# control keys, use:
# Option "XkbOptions" "ctrl:swapcaps"
# Or if you just want both to be control, use:
# Option "XkbOptions" "ctrl:nocaps"
#
Identifier "Keyboard0"
Driver "keyboard"
Option "XkbRules" "xfree86"
Option "XkbModel" "pc105"
Option "XkbLayout" "us"
EndSection

Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/psaux"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "no"
EndSection

Section "InputDevice"

# If the normal CorePointer mouse is not a USB mouse then
# this input device can be used in AlwaysCore mode to let you
# also use USB mice at the same time.
Identifier "DevInputMice"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "no"
EndSection

Section "Monitor"
Identifier "Monitor0"
VendorName "Monitor Vendor"
ModelName "Dell E551a"
DisplaySize 270 200
HorizSync 30.0 - 54.0
VertRefresh 50.0 - 120.0
Option "dpms"
EndSection

Section "Device"
Identifier "Videocard0"
Driver "i810"
VendorName "Videocard vendor"
BoardName "Intel 865"
EndSection

Section "Screen"
Identifier "Screen0"
Device "Videocard0"
Monitor "Monitor0"
DefaultDepth 16
SubSection "Display"
Depth 16
Modes "800x600"
EndSubSection
EndSection

Section "DRI"
Group 0
Mode 0666
EndSection