Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Please tell me what maker, and what model #, of scanner you have.
Try opening up the scanner part of the machine (I could be much more specific if I knew the maker and model number of this machine, of course), and examine it for any fouled, broken, jammed, or otherwise out-of-order paper presence sensing switches. That is most likely to be the current problem.