Theres a few things you can try:
1. Manual Clean : Try taking the cartridges out, take the back off (that bit you can unlock (I'm guessing this model has that feature)), and then get a cloth and clean out any crap. Try to clean as best you can around where the cartridges and paper meet.
2. Automatic clean : HP's toolbox; align cartridges, clean cartridges, test pages etc.
Try switching off your computer and printer, then switch the printer on before switching on the computer. Make sure the paper is pushed in as far as it can go i.e. from the bottom and side.
I had a similar problem at work before so I did this sort of thing and eventually it worked.