An X xpert required!

[#1]

Had a few anxious hours recently.
Yesterday we were granted a brief power cut - and I had the impression that it corrupted my /etc/X11/xorg.conf file.
I think I'm wrong though 
I think what actually happened is that my video card (nvidia) can no longer recognise my screen.
It would only work at a resolution of 640 x 480 
It still can't do recognition  - but I've managed in a horrible way to get it working at 1280 x 1024 at 96 x 96 dpi at a Depth of 24
I'm quite confused about the distinction between dpi and resolution - what does this mean?
Furthermore...
Ubuntu has an option for setting Nvidia X Server settings (Under Administration) and
a setting under preferences (per user) for screen resolution.
Like I say, I have somehow magicked the problem away - using the CLI  but I'd like to know what was going on.

[#2]

dpi is dots per inch for your fonts.  resolution is the pixels across and down your screen.
if you can get to a text login, login as root and type video.  this will allow you to set up your video card again get back into your user.  if it isn't exactly what you want, you can then go to whatever control centre you have and set up your graphical server.

[#3]

I'm going to let sleeping dogs lie - but I'll make a note of the video command. Thanks.
I'm still confused about dpi - is the dot size measured in pixels or is it really dots per inch?

[#4]

it's a legacy of the print world and dot matrix.  printing talks in terms of 'point' in defining size.  digitisation required a slight modification.  in order to get 12pt onto paper, it had to be so many dots tall by so many dots wide.
resolution is talking about something different.  it's the number of pixels horizontally and vertically that fill your screen.  they are not dots, but small rectanges divided into 8 compartments, each describing a colour in the red, blue, green and greyscales.

[#5]

Quote from: axisofevil

Had a few anxious hours recently. Yesterday we were granted a brief power cut - and I had the impression that it corrupted my /etc/X11/xorg.conf file.

It is probably unlikely, unless you were at that moment in time writing to this file and the crash caused it to corrupt.  Boot a LiveCD, make sure that the partition(s) are not mounted and run fsck -C or fsck.ext3 or the appropriate command for your fs.

Quote from: axisofevil

I think what actually happened is that my video card (nvidia) can no longer recognise my screen.

Could it be that the nvidia driver/module was corrupted?  Could it be that the card itseld was borked as a result of the power cut?

Quote from: axisofevil

It would only work at a resolution of 640 x 480  It still can't do recognition  - but I've managed in a horrible way to get it working at 1280 x 1024 at 96 x 96 dpi at a Depth of 24 I'm quite confused about the distinction between dpi and resolution - what does this mean?

resolution is the size of your screen (width x height), while dpi refers to your font size.  96x96 is the default MSWindows font size and may make your browser show websites fonts like the MSWindows abomination of an Internet browser.
Your distro would have some means (could be a script) which will regenerate an xorg.conf file.  Alternatively, you may need to reinstall xorg and, or your nvidia module.
HTH.