Hook up an external monitor and see if you get a picture. If you do then you can most likely fix any software issue you would have, but if the screen is not coming on AT ALL it could be hardware related. If you're lucky there is a magnetic switch in the hinges that will cycle the screen on and off when the lid is open, try to fully open the screen as far as it can go and close it and do it again and see if it comes on. Next luckiest would be that the screen connection wire came loose, then the inverter board, that's a cross between luck and cost.
I try not to stand on my notebook. There's times when I really need to reach something and the extra few inches comes in handy so I do, but as a rule of thumb, tell your family member that if they have to stand on your notebook, try to stand as close to the outside edges as they can. Whenever possible, stand on the notebook when it is open to avoid crushing the screen... keyboards are a lot cheaper.
yes most of the likley causes have been covered already by xstec . Try toggle your notebook screen and external screen by using the Fn and F10 keys. You may have broken the screen's backlight which is probably a very thin flourescent tube (I kid you not) very fragile . Look very carefully at the top left of the screen to see if you can see the curser. Try turn the lights off whilst looking. If you see something in the background the backlight or the inverter has gone.
If you get some beeps and led's you have a chance of recovery however your AVG update may have corrupted your boot files . Try booting from another hard drive or from the floppy if there is one or from the DVD drive with your Windows disc see what happens.
If you want to recover your data then you need to remove the hard drive and attach it to any computer using a special USB 2.5" connector. Plenty on ebay for about £5.00
Another useful tip is to use two laptops to stand on which will distribute the weight evenly