If you are looking at a blank screen and you don't know what to write the problem is that you are looking at a blank screen which isn't telling you what to write.
Go out for a walk. Look at people, wonder what they are doing. Ask yourself what they would be doing if they were in your story. Writer's block is just an indication that you need to look for ideas. Don't worry if they are good ones or not. At least you will be writing again.