I am working with 2 IBM T43P laptops, both had bad displays. Now neither will Post/Boot without an External Monitor connected to the VGA port.
I have purchased a Brand New display, Model is identical to what was installed. I know IBM is very specific about parts that are allowed to be used on their laptops.
I have tested both sticks of RAM is a working laptop without issues, both passed memory diagnostics.
I made sure the switch that detects whether or not the top is closed was not blocked or stuck.
I can get both laptops to boot with an External Monitor, every time I hit FN + F7 (Video Output Select) to switch too the internal LCD output that laptop instantly turns off.
I have switched out the inverters on both laptops also.
I have removed the Bluetooth, Wireless Card, the PCIMCIA bay, and CD-ROM to make sure it wasn't a hardware malfunction issue.
I have reseated video ribbon on both monitor and board several times making sure it's not a connection issue. Also checked the ribbon for breaks or bare wires.
I've done a complete BIOS reset, removing the CMOS battery, laptop battery, and external power... plus holding the power button for 10 secs.
No matter what I've tried I cannot get the system to boot without an external monitor attached (which works 100% without error) soon as the output is switched or the external VGA is removed the laptop completely shuts down and will not reboot until all power is removed first.
I'm completely out of ideas at this point.