I have an IBM Thinkpad T40 type 2374. On power up, the screen shows the IBM logo, then get black with small horizontal lines close to the bottom screen. When window is running, it shows fuzzy vertical strips, shadow like across the screen. When I switch the screen on/off, sometime it show window properly for a second, and flip back to vertical fuzzy strips. It works fine with external monitor. As I know, this could be the video circuit on the main baord , the lcd cable or the lcd screen. Is there a way to test to see what is it? Since this model doesn't have video card, the video chip is on the main board, how can I identify which one?

Thanks.