The only thing I can remember from the movie was an alien like creature that held an human and had a tentacle or something like that in to him and talked to some other humans through the guy he holding. I don't know how old the movie is but it must be pretty old because I was a child when my uncle showed it to me and I'm 20 years old now. I know it's a very bad desription but I really hope that someone can tell me the name of the movie. Thankfull for answers!

Probably wrong but in killer klowns from outer space a clowns "puppets" a guy.

Possibly Independence Day. I got this clip from IMDB, unfortunately it ends right before the alien uses the long haired scientist to 'talk' through the glass to everyone watching. (maybe it will ring a bell to you?)

Independence Day Clip (Alien Surgery) - IMDb

I got this off the parent advisory portion of IMDB for Independence day too - it references the scene you were describing:

"Moderate: The scene in which the alien uses its tentacles to make a dead scientist 'talk' for it may frighten younger viewers."

Independence day it is! Thaanks so much!

:)