Inspiron 6000 display problems

I am having some major issues with the screen on my Inspiron 6000 and I just wanted to see if anyone has run into a similar issue and what they had to do to fix it. A couple of months ago, I started to get white horizontal lines across the screen that would flicker off and on during the boot up into windows. After a couple minutes they would go away. In the last couple of days the problem has gotten much worse. A lot more lines appear all over the screen and at times the whole screen becomes unreadable. Also the lines do not go away like they used to. I have run the dell diagnostic and it doesn't report any errors. All the display tests work fine as well. I have also hooked the laptop up to an external monitor and the problem doesn't happen on the external monitor. I am wondering if this is a loose wire or something or if I need to replace the whole LCD screen. Has anyone run into this problem? Thanks in advance for the help.