Wheneve i try to use the video funcionality, the .mov gets too dark.
The movie get so dark that it is not possible to watch.
I tryed many things but only with lots of light (sunny day), I get a good movie.
Does anybody knows if its possible to fix this?

I have no experience with this model , but have you tried going to nikon's tech site to look for fixes and or firmware update. My model, CP4300, had a bug that would cause it to turn offf when plugged into a TV and nikon released a firmware upate.

By the way, your pictures look fine right? You might want to calibrate your monitor to ensure it's not your monitor setup incorrectly.