If there is no paper in the feeder, this could likely be solved by the old "turn it off and on again". If there are no mechanical issues, then resetting the device firmware could free it from the nonexistent "paper jam."
If this doesn't work, there is likely something going on with the mechanical bits. Here is the manual: http://h10032.www1.hp.com/ctg/Manual/c03226612 and if you straight to page 126, there are some handy steps as to how to make sure the feeder and carriage are free. Go through the steps, then reset, and I bet all will be well.
Best of luck!