I decided to make another try today after some reading and googling the internet.
I started windows with my old 4GB memory and changed the bootconfiguration with msconfig. I typed manually in max memory tp 16384 MB and saved the settings. Then I turned it off and inserted the 16GB ram again. Then it started really but when looking at the properties of my computer it says 16 GB installed but I can only use 2,16GB. So I opened msconfig again and changed the settings once more and restarted. Now it says 16GB installed but I can use 14,2GB so I guess it is ok now for some strange reason. I suppose the lost 1,8GB is for the system ?? Do I dare to turn it off again :-) what will it say next time ?
I am so happy and greatful for all your help, I really really appreciate it and I hope my solution will come to use for someone else with same problem.
Thank You all :-)