Inspiron 8000 Black screen

I have an 8000 that when boots shows a red screen then disapears altogether !! I bought  a "used tested complete 15' lcd screen with lid" Guy swears ot worked fine when he shipped it. Now I  slid the hinges in screed it down installed the cable and screwed that down and booted. Nothing not a glimmer!! Hooked up to the KVM switch I can see everything fine on my external monitor. I went to dell and d/l and installed the latest video driver for the ATI and I still have nothing!! Am I missing something? Video has been set to "never off on batt or AC power." Maybe the seller is less than honest? He has great feedback no negs at all