What happens is these Nvidia GPU's used on a variety of laptops run very hot and are known as a "Faulty" range of GPU's, between consumers not dusting out their laptops enough and placing them on surfaces with very little airflow (IE bed, cushion, lap) they get superheated which causes the micro-solder joints to melt and a result is 1 or more of those pins lose their connection with the motherboard.
The end-result is no video and black screen with a confused bios and the equivalent of a very expensive doorstop. What you just did on my advice was the same thing as an "X-clamp" fix for an Xbox-360 which is to overheat the chip on purpose in order to "reflow" the solder, the pressure re-seats the pins to a connected state and results in a fixed GPU.
Be sure to dust out the fan/heatsink very well and get yourself a tube of Arctic Silver heatsink paste from Radio Shack, make sure it is a Silver-Oxide compound as the stuff from the manufacturer of the laptops is mostly polymer based and is a poor excuse for heat-transfer paste.
First use q-tips and rubbing alcohol (at least 91% strength) and clean the contacts on both the gpu/cpu and the heatsink contacts, then apply a very small amount of heatsink paste to the Die on the GPU and CPU, using a business card or something similar flatten it out so a very consistent layer is across the die, then rescrew the heatsink and go from there. (in my case i had to do the reflow trick again because i had not waited long enough the first time and seating/re-seating the heatsinks after cleaning and pasting caused the connection to fail again, but even with heat compound on it lifting the sink caused it to overheat enough to press it down again and re-create the fix)
Have fun using your newly revived computer.
Saiber77