IBM ThinkPad X31 I can see windows booting on my X31 laptop, but it's very dim. I don't think it's a switch problem, so I...

I got my IBM X31 fixed with the same issue. Turns out to be that the connections on the port needing bending back into shape and spraying with switch lubricant. Now it works fine. Try applying pressure on the power connector to see if power comes on intermittently. If so, it might be the same issue as mine.