How do I reset my display settings from the command line?

I'm running 12.10 on a dell e5400 laptop and I used xrandr to get the dual monitors working that I connect through a laptop dock. I used xrandr again to switch back to the laptop display when I undocked. The problem is, after a restart, the laptop seems to want to come back up with the dual monitor configuration and the laptop screen stays blank. I can boot into single user mode but I'm not sure what to do from there to get the display settings reset. Any ideas? There's no xorg.conf file so I'm not sure where the settings are stored anymore.

Thanks.

Here's what worked for me:

In a terminal, type:

xrandr

You'll see various modes, which look something like this:

eDP1 connected 1440x900+0+0 (normal left inverted right x axis y axis) 30mm x 179mm
   1440x900       60.0*+   59.9  
   1360x768       59.8     60.0  
   1152x864       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
   2560x1440_30.00   29.9  

In my case, HDMI1 was the external monitor.

So, I just ran:

xrandr --delmode HDMI1 2560x1440_30.00

Now, when I plugged in the external monitor, it was as if it was the first time Ubuntu saw it.