As Hellashot says, if part of the screen is different to the rest and/or the whole thing has gone very dark, it's likely undergone significant damage and I suspect is probably beyond economic repair. These monitors are pretty much solid state - there's nothing in them that's going to get knocked out that you can fix, unlike contrast and brightness controls in many (particularly older) CRT monitors, which are ordinary potentiometers.
I wonder if you've suffered damage to the backlight, considering that you're describing the picture as dark. It's unlikely that such damage is as simple as a wire or two coming loose and I wouldn't want to be poking around with cold cathode lamps. The best thing, sadly, is likely to be writing the situation off to experience and investigating whether your household insurance covers accidental damage.
It is just possible that you've loosened one or more connectors internally, and you may be able to reconnect them, but if you don't know what you're doing, I wouldn't just open it up to have a go. I feel this is unlikely anyway.
Auto adjust and similar indicates you're using a LCD monitor that connects via a D-sub analog connector. If you have to replace the monitor, try to look for a monitor with a DVI input, which is a digital connector for LCD monitors. If you don't already have a DVI output on your graphics card, a suitable replacement card is inexpensive if your computer uses an AGP or PCI-E graphics card. I recently upgraded one of my computers to a DVI capable AGP card for GBP30.
Meanwhile, as PacAce mentions, if you have colour calibration kit, use it. However, if you've suffered backlight damage, no calibration or settings adjustment is going to rescue things.
David
