I have managed to establish that my Dell laptop 6400 does not have a problem with generating display data. Connecting an external monitor provides a perfect picture. There is data going to the LCD screen but it is very dark. A web search suggests that I replace the inverter. I have done that but still have the problem. I have checked to see whether the new inverter was connected up properly and it is. I have run Dell Diagnostics and there is an error: "2000-0322 Error accessing the LCD inverter" On reflection, I should have run the diagnostics before buying a new inverter!
Whilst checking to see whether I had pushed the connecters to the new inverter fully home I managed to get the display working, but I lost it again. This suggests to me that the new inverter is working ok and maybe the old one was as well! I also checked the connections behind the LCD display, they are OK. So I am now thinking of what I need to do to check whether the power supply to the inverter is stable.
If my reasoning is correct what do I need to do to check the power supply to the inverter? But also, is there some other factor that clouds the issue?