Inspiron 8500 LCD/Video Issue

I am having issues with my Inspiron 8500. When I boot it up using it's LCD I get a "Garble Fence" going across the screen and the computer locks up. When I connect it to an external monitor and use dual screens (external and lcd) I can boot it up with no problem and use it like normal. The issue is only when I try to use it without an external moniter. Some times it will boot into windows but will soon lock up. When I have it using battery power it also works fine. It's kind of strange. Thanks in advance for the help!