I just installed Ubuntu 16.04. After installing and login. I can't do anything. Only the classic wallpaper of the Ubuntu and one message error which is hidden after some seconds.Error say "Ubuntu 16.04 has experienced internal error". It disappear and appear again and again. And I also can't connect wifi. Please help me.
Well since you just installed Ubuntu 16.04 you won't loose anything by installing it again. I'd suggest that and paying close attention to any messages during installation. If nothing new is discovered I would install 14.04 which has a longer period of testing and debugging.
It would also be helpful if you listed your Desktop / Laptop make, model, configuration, etc. Other people using the same hardware might provide insight based on their experience.