The picture on the door isn't a keyboard, nor is it a robot, nor is it a microwave, nor is it the Window's Start Menu.
What do you think "The fifth was combined" is referencing?
What normally gets combined when reading through a page of text?
What do you think "Should be there but now isn't" is referencing?
When things were combined, or shortened, something was removed.
Did you get two letters that seem to repeat?
What else do those letters look like?
Could they possibly be representing numbers?
A computer would be able to understand it.