Paper Jam No book of instructions with my model. Number is HP Officejet J5780 All-in-One. Cannot even shut the printer off till tomorrow without fixing the jam now.

printer keeps jamming when i try to print but there is no paper jam.

Have you tried these solutions?
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00829028&cc=us&lc=en&dlc=en&product=3301296&tmp_track_link=ot_search

Download the manual from HP website http://h10025.www1.hp.com/ewfrf/wc/manualCategory?cc=au&lc=en&dlc=en&document=&product=3301296
Page 127 covers clearing paper jams.

Usually, by disassembling the printer. To change cartridges and clear some paper jams, lift the top.

The sensor detecting the movement of the paper may have failed. As it requires expert service and replacement of the sensor better to contact the Service person.

lift the feed area and look at the small glass plate where the auto feed paper is actually scanned. That needs a good cleaning. Since the paper runs across it even a tiny little obstruction such as paper left from a paper jam or a dot of ink from that pen you used to unstick that last paper jam (maybe its just me??). That one dot turns into a line when the paper rolls across it. Clean well and the line will dissappear.

To start with first try a reset:

Unplug the power cord from the All-In-One as well as the power outlet when there is still power in the All-In-One. and wait for atleast 1Min
Plug the power cord directly to a wall outlet without surg protector. (if possible connect it to a different power outlet)
Before connecting the power cord to the All-In-One press and hold the # and no 6 button and then insert the power cord, do not release the keys
until you see a message a reset (if the screen goes blank then release the keys and turn the power on)

Then check and see

If not try the link bellow:
http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&cc=us&docname=bpu00804&dlc=en&product=79477

Good Luck please let me known if nay problem.

Make sure that you have the duplexing option turned on in your printer configuration. The "OK" button is right below the window that shows the date and time. Have a look here:

http://h71016.www7.hp.com/html/interactive/j5780/model.html?jumpid=in_r2910_3d/PDI/j5780%7Cshowcase%7Cflash

I had same problem. Have you checked for paper-jam from the back, as sometimes a small piece of paper may be still jammed in. Pull open the door and check. Do not pull jammed paper from the front as this disturbs the rollers and printing process. I di this, and have had to buy a new printer.!!

The paper sensor flag is probably stuck or broken. The part number is C7309-40013.