i had problem with my Sony Vaio not powering up at all (no light etc). I tried everything (wiggling the power adapter, removing battery and pressing start, removing RAM), and occasionally it would start up and work for a few hours/days. Lately, it just wouldn't respond to any of these "fixes", so I read this site with much interest and tried the upside down fix but alas that had no success. Out of sheer desperation I just plugged an external monitor into the side of the laptop and the machine now starts up again, take the cable out and the machine instantly crashes. I don't know whether it's the effect of the external monitor, or just having the cable in the socket, as I haven't got a spare monitor cable to try it with (my monitor's cable is built in).
I guess it's not a practical solution, but it may help in an emergency!