My T400 shuts down instantly when I plug a non Lenovo monitor in. What should I do? If I shut down the computer, and then try starting the computer with the monitor plugged in, the computer shuts down almost instantly after I press the power button. In each case, I have to unplug the computer, and remove the battery, before I can try turning the computer on again. I have installed the latest power manager, video drivers and BIOS. On the odd occasion, I am able to plug in my monitor without the computer shutting down. This happens when using integrated and discrete graphics.
This suggests a short in the display cable. Check for bent pins on the connector, and try to test with another external display and cable. If the system works well with another external display, the problem can be isolated to a defective VGA cable. Replace the cable.