No video at all, even with external monitor

The macbook pro turns on but there is no video signal on the screen. At first I tried a workaround connecting an external monitor but nothing seems to come out of the laptop.

Then i tried wakeing it up as an external harddrive of another macbook and after sime tries i could see my data in the hdd from the other laptop.

How can I determine if it is a nvidia problem or something else?

Thank you in advance, Andrea