Welcome. I am Mike, an experienced field technician. We are now connected together on this convenient website where I am able to help you.
First suspect is the paper sensor flag. It is made of plastic and is VERY common to bend/break. Usually has to be replaced. Here is a picture of the part:
Let me know if you want to attempt replacing it yourself, otherwise you will need a printer technician.
Before you go please take a moment to submit at least a 3 star rating at the top of this page. Then if you still need help you can reply back and I will be happy to assist you further.