Hello and thanks for using JustAnswer.
This is not an unusual problem with the large HP printers.
First be sure ALL the jam is cleared.
Sometimes even a little shred of paper left in a tray or under the fuser will mess up the works. By the way, fuser is HOT for several minutes after unplugging the printer so be VERY careful.
If you have the manual for the printer, the directions are on pages 136 - 149
If you don't have the manual handy, here's a link: HP
Let me know if a thorough search of the machine for that scrap of paper isn't the problem and we can dig a bit deeper, but most of the time it's a sneaky shred of paper.
Thanks,
Harvey Allen
Computer Support Specialist
Adult Education software instructor since 1980's. Computer consultant since 2005.