On the day Raring Ringtail came out, I upgraded my 12.10 desktop to 13.04 and have been very pleased with it. This morning I saw the notice that security updates were available popped up, so I allowed it to download and install these updates. The updates required rebooting. Upon reboot, the computer went into a low-res, 640x480 mode with my display defaulting to a 'laptop'. I have been unable to figure out why and how to return my settings back to their original 1920 x 1080 settings. I just want to get my computer back to the way it was before these security updates were installed. Can anyone help me?

Thanks in advance for your help.