I am running Debian 8 on a Toshiba Satellite laptop. When at home I connect my laptop to an external monitor through an HDMI cable.
My laptop's monitor has recently stopped supporting any display mode except for 640x480. Here's the output of
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192 LVDS1 connected (normal left inverted right x axis y axis) 640x480 59.94 VGA2 disconnected (normal left inverted right x axis y axis) HDMI1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 600mm x 340mm 1920x1080 60.00*+ 50.00 59.94 1920x1080i 60.00 50.00 59.94 1680x1050 59.88 1400x1050 59.95 1600x900 59.98 1280x1024 60.02 1440x900 59.90 1280x800 59.91 1152x864 59.97 1280x720 60.00 50.00 59.94 1024x768 60.00 800x600 60.32 720x576 50.00 720x480 60.00 59.94 640x480 60.00 59.94 DP1 disconnected (normal left inverted right x axis y axis)
As you can see, the only mode available for my laptop's monitor is 640x480, even though it usually supports many modes up to 1366x768.
This is not a hardware problem because my GRUB menu uses 1366x768 just fine.
I think the problem started after I messed with my graphics card settings. I was trying to get Debian to use my NVIDIA graphics card so I ran the command
nvidia-xconfig. The X Window System would not resume on startup however (probably because I do not have the required packages to use my NVIDIA graphics card), so I modified
/etc/X11/xorg.conf so that x-org would use my Intel graphics card instead.
I believe that ever since my laptop's monitor has stopped supporting higher resolution display modes.