Perhaps TonyV is on the right track by asking if your print cartridges are ok.
I have an HP printer and a few weeks back I had a similar problem.....It wasn't printing everything it should have been. I had a problem trying to establish the cause because the machine was indicating an ink problem with both cartridges. So I ended-up changing both and everything then became as it should be.......Pricey if you use HP cartridges...I get on alright with recycled/refilled items.