I have a dell inspiron 1525 and I am having screen problems. when computer is plugged in it works fine but when I un plug it and try and run it off the battery the screen goes so dark I have to have room lights on to see it. when I try and turn it up it wont work so I try to plug it back it but that wont work all I can do is turn it off and try it back on to see the screen

Go to Control Panel, select Power Options. Click the "High Performance" circle.

This can be caused by a number of reasons more than likely though it's a hardware issue.

The first thing I would try to resolve this issue is to update the bios to the latest firmware.

You can download it here.

Make sure all other programs are closed before you run the update. Also make sure you don't do ANYTHING else or move the computer during the update

Let me know if that resolves your issue otherwise it's plan B ;)