The first thing you should do is "power cycle" the device. This is a fancy way of saying to switch the printer off at the wall, and then turn it back on.
Yep, it's that complicated.
It's amazing how many problems this simple process can solve, though. And that goes for any electrical device: printers, mobile phones, internet modems etc.
To be absolutely sure the memory has been reset on the printer, turn it off and pull the plug out, then wait 10-15 seconds before you turn it back on.
The other thing to try would be to check the hardware of the printer. Check for paper jams and the levels in the paper trays. Also check the ink levels in the cartridges.
You can usually check this on the computer the printer is hooked up to via the printer settings.
