If you just put new ink in your printer, and your printer spews out one of those ugly test sheets, you know it works fine. Then you go to print off something that actually matters, and your printer does: nothing. It's not broken, it's just being a cussy little chunk of technology that is intent on making your life harder.
To fix it: Cancel your print job, then click print again. This time, gently stroke your printer and whisper words of encouragement. It should work just fine.