everytime i change something i get asked to log in again so it doesn't update

I have been trying to update my website since yesterday, but everytime i change something i have to log when I want to update so wordpress does not save my changes.

I am going crazy about this, because I cannot do anything! I spend 10 minutes on uploading a slidebar only to see it was for nothing.

What happens there? Do I have a virus? Or am I doing something wrong?

I don’t get it! Please help me!