Hi There,
You will need to make some modifications to your /etc/X11/xorg.conf file (it is where all your video settings are). You will need to add a "ModeLine" that tells the monitor what resolution to use.
You can find more information on the WIKI, you can also search for the modeline (resolution) you are looking for.
Also, be sure you review you xorg log file (it is located /var/log/Xorg.0.log)
You will also need to make sure your display section is setup to display the resolutions you want.
SubSection "Display"
Depth 15
Modes "1144x644" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 16
# Modes "1144x644" "800x600" "640x480"
Modes "ATSC-720-60p" "1144x644" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 24
# Modes "1144x644" "800x600" "640x480"
Modes "ATSC-720-60p" "1144x644" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 32
# Modes "1144x644" "800x600" "640x480"
Modes "ATSC-720-60
Below is an example from my xorg.conf file.
Section "ServerLayout"
Identifier "XFree86 Configured"
Screen 0 "Screen0" 0 0
InputDevice "Keyboard0" "CoreKeyboard"
# PS/2 Mouse not detected
# InputDevice "Serial Mouse" "CorePointer"
InputDevice "USB Mouse" "CorePointer"
EndSection
Section "ServerFlags"
Option "AllowMouseOpenFail" "true"
EndSection
Section "Files"
RgbPath "/usr/share/X11/rgb"
ModulePath "/usr/lib/xorg/modules"
FontPath "/usr/share/fonts/X11/misc:unscaled"
FontPath "/usr/share/fonts/X11/75dpi:unscaled"
FontPath "/usr/share/fonts/X11/100dpi:unscaled"
FontPath "/usr/share/fonts/X11/Type1"
FontPath "/usr/share/fonts/X11/Speedo"
FontPath "/usr/share/fonts/X11/PEX"
# Additional fonts: Locale, Gimp, TTF...
FontPath "/usr/share/fonts/X11/cyrillic"
# FontPath "/usr/share/fonts/X11/latin2/75dpi"
# FontPath "/usr/share/fonts/X11/latin2/100dpi"
# True type and type1 fonts are also handled via xftlib, see /etc/X11/XftConfig!
FontPath "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
FontPath "/usr/share/fonts/truetype"
FontPath "/usr/share/fonts/latex-ttf-fonts"
EndSection
Section "Module"
# Comments: see
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=346408
Load "dbe" # Double Buffering Extension, very important.
# Load "dri" # This shouldn't be available choice if user has selected driver vga, vesa or nv.
Load "glx" # GLX Extension.
Load "freetype" # Freetype fonts.
Load "type1" # Type 1 fonts
Load "record" # Developer extension, usually not needed
# Load "extmod" # This is okay, but if you look into "man xorg.conf" you'll find option NOT to include DGA extension with extmod, and for a good reason.. DGA causes instability as it access videoram without consulting X about it.
SubSection "extmod"
Option "omit xfree86-dga"
EndSubSection
# Load "speedo" # Speedo fonts, this module doesn't exist in Xorg 7.0.17
# The following are deprecated/unstable/unneeded in Xorg 7.0
# Load "ddc" # ddc probing of monitor, this should be never present, as it gets automatically loaded.
# Load "GLcore" # This should be never present, as it gets automatically loaded.
# Load "bitmap" # Should be never present, as it gets automatically loaded. This is a font module, and loading it in xorg.conf makes X try to load it twice.
EndSection
Section "InputDevice"
Identifier "Keyboard0"
Driver "kbd"
Option "CoreKeyboard"
Option "XkbRules" "xorg"
Option "XkbModel" "pc105"
Option "XkbLayout" "us"
EndSection
Section "InputDevice"
Identifier "PS/2 Mouse"
Driver "mouse"
Option "Protocol" "auto"
Option "ZAxisMapping" "4 5"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "true"
Option "Emulate3Timeout" "70"
Option "SendCoreEvents" "true"
EndSection
Section "InputDevice"
Identifier "USB Mouse"
Driver "mouse"
Option "Device" "/dev/input/mice"
Option "SendCoreEvents" "true"
Option "Protocol" "IMPS/2"
Option "ZAxisMapping" "4 5"
Option "Buttons" "5"
EndSection
# Auto-generated by KNOPPIX mkxf86config
Section "Monitor"
Identifier "Monitor0"
Option "DPMS" "true"
Option "UseEdidDpi" "FALSE"
Option "DPI" "100 x 100"
VendorName "SAM"
ModelName "SAM4d72"
HorizSync 15.0 - 46.0
VertRefresh 59.0 - 61.0
# HorizSync 28.0 - 78.0 # Warning: This may fry very old Monitors
# HorizSync 28.0 - 96.0 # Warning: This may fry old Monitors
# VertRefresh 50.0 - 75.0 # Very conservative. May flicker.
# VertRefresh 50.0 - 62.0 # Extreme conservative. Will flicker. TFT default.
# These are the DDC-probed settings reported by your monitor.
ModeLine "640x350" 31.5 640 672 736 832 350 382 385 445 +hsync -vsync
ModeLine "640x400" 31.5 640 672 736 832 400 401 404 445 -hsync +vsync
ModeLine "720x400" 35.5 720 756 828 936 400 401 404 446 -hsync +vsync
ModeLine "640x480" 25.2 640 656 752 800 480 490 492 525 -hsync -vsync
ModeLine "640x480" 31.5 640 664 704 832 480 489 491 520 -hsync -vsync
ModeLine "640x480" 31.5 640 656 720 840 480 481 484 500 -hsync -vsync
ModeLine "640x480" 36.0 640 696 752 832 480 481 484 509 -hsync -vsync
ModeLine "800x600" 36.0 800 824 896 1024 600 601 603 625 +hsync +vsync
ModeLine "800x600" 40.0 800 840 968 1056 600 601 605 628 +hsync +vsync
ModeLine "800x600" 50.0 800 856 976 1040 600 637 643 666 +hsync +vsync
ModeLine "800x600" 49.5 800 816 896 1056 600 601 604 625 +hsync +vsync
ModeLine "800x600" 56.3 800 832 896 1048 600 601 604 631 +hsync +vsync
ModeLine "768x576" 35.0 768 792 872 976 576 577 580 597 -hsync +vsync
ModeLine "768x576" 42.9 768 800 880 992 576 577 580 601 -hsync +vsync
ModeLine "768x576" 45.5 768 808 888 1008 576 577 580 602 -hsync +vsync
ModeLine "768x576" 51.8 768 808 888 1008 576 577 580 605 -hsync +vsync
ModeLine "768x576" 62.6 768 816 896 1024 576 577 580 611 -hsync +vsync
ModeLine "800x600" 68.2 800 848 936 1072 600 601 604 636 -hsync +vsync
ModeLine "1024x768" 113.3 1024 1096 1208 1392 768 769 772 814 -hsync +vsync
ModeLine "1152x864" 81.6 1152 1216 1336 1520 864 865 868 895 -hsync +vsync
ModeLine "1152x864" 119.7 1152 1224 1352 1552 864 865 868 907 -hsync +vsync
ModeLine "1152x864" 143.5 1152 1232 1360 1568 864 865 868 915 -hsync +vsync
ModeLine "1920x1200" 193.2 1920 2048 2256 2592 1200 1201 1204 1242 +hsync -hsync
ModeLine "ATSC-480-59.94i" 12.0 640 664 736 760 480 484 492 525 interlace
ModeLine "ATSC-480-60i" 12.0 640 664 736 760 480 484 492 525 interlace
ModeLine "ATSC-480-59.94p" 23.9 640 664 736 760 480 484 492 525
ModeLine "ATSC-480-60p" 23.9 640 664 736 760 480 484 492 525
ModeLine "ATSC-480a-59.94i" 12.0 640 664 736 760 480 484 492 525 interlace
ModeLine "ATSC-480a-60i" 12.0 640 664 736 760 480 484 492 525 interlace
ModeLine "ATSC-480a-59.94p" 23.9 640 664 736 760 480 484 492 525
ModeLine "ATSC-480a-60p" 23.9 640 664 736 760 480 484 492 525
ModeLine "ATSC-720-59.94p" 74.2 1280 1320 1376 1650 720 722 728 750
ModeLine "ATSC-720-60p" 74.2 1280 1320 1376 1650 720 722 728 750
ModeLine "720x480" 27.0 720 736 798 858 480 489 495 525 -hsync -vsync
ModeLine "1144x644" 74.2 1144 1320 1360 1648 644 685 690 750 +hsync +vsync
# ADDED THIS SECTION FROM 20
Option "DPMS" "true"
Option "UseEdidDpi" "FALSE"
Option "DPI" "100 x 100"
Option "TVStandard" "NTSC-M"
# Option "ConnectedMonitor" "TV"
Option "NoLogo" "1"
EndSection
Section "Device"
### Available Driver options are:-
# sw_cursor is needed for some ati and radeon cards
#Option "sw_cursor"
#Option "hw_cursor"
#Option "NoAccel"
#Option "ShowCache"
#Option "ShadowFB"
#Option "UseFBDev"
#Option "Rotate"
Identifier "Card0"
# The following line is auto-generated by KNOPPIX mkxf86config
Driver "nvidia"
VendorName "All"
BoardName "All"
# BusID "PCI:1:0:0"
EndSection
Section "Screen"
# put options here
Identifier "Screen0"
Device "Card0"
Monitor "Monitor0"
DefaultDepth 24
Option "NoLogo"
#PF investigate Option "MetaModes" "1144x644"
# Option "MetaModes" "1280x720" # For 720P
#pf test15 Option "ConnectedMonitor" "TV"
# Option "TVStandard" "NTSC-M"
Option "TVStandard" "HD720p" # For 720P
Option "UseEvents" "True"
#Option "sw_cursor"
#Option "hw_cursor"
#Option "NoAccel"
#Option "ShowCache"
#Option "ShadowFB"
#Option "UseFBDev"
#Option "Rotate"
SubSection "Display"
Depth 15
Modes "1144x644" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 16
# Modes "1144x644" "800x600" "640x480"
Modes "ATSC-720-60p" "1144x644" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 24
# Modes "1144x644" "800x600" "640x480"
Modes "ATSC-720-60p" "1144x644" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 32
# Modes "1144x644" "800x600" "640x480"
Modes "ATSC-720-60p" "1144x644" "800x600" "640x480"
EndSubSection
EndSection
Hope this helps