I started to print something, then immediately realized that I had no paper. I quickly grabbed some and put it in the printer. However, the machine had already realized that there was no paper. Now it won’t say that there is paper in there, and simply sit and waits, frustrating me.
Cancel the job in the Print Manager if it’s still queued, power cycle the printer (with the paper loaded, of course) and reprint the job. If that still doesn’t work, you might need to reboot your computer, as well. I’m assuming some flavor of Windows here; if you have something else like Mac or Linux, someone else will have to walk you through it.
“…Did you eeeever knooow that you’re my heeero…you are the wiiiiind beneath my wiiiings…”
Huzzah, and thank you!
Well…it printed out one page…then promptly denied there was any paper, so I sang too soon (and too off key, also). I will reboot and report back. 
You didn’t say what brand printer you have, but at least on HP models, when they are out of paper, they will flash a little light over one the buttons on the printer. After you have loaded more paper, hit the button. No need to cancel the job or reboot.
Yeah, I should have mentioned that: it’s a Canon BJC-2110
There might be a problem with the paper feed sensor. If you have a can of compressed gas dust spray with an extension tube for the nozzle, you can try taking all the paper out and spraying in as far down in the paper feed as possible, in case dust or paper shreds are interfering with it. Depending on the printer you have, you might need to remove a tray to get to the sensor, or lift up the cover. Keep the can upright and spray in short bursts, so you don’t expel any of the contents in liquid form, which can sometimes damage plastic parts. When you put the paper back in, jiggle it back and forth a little to work the sensor mechanism–sometimes the mechanicl switch types can get a little sticky. It could also be an optical sensor, in which case there’s little you can do unless you can get to it to clean it off with a swab and some alcohol. If you’re lucky, the dust spray will blow it clean. In any case, once you’ve done everything you can reasonably do to ensure the sensor is clean, then power cycle the printer again.
Some printers will make you explicitly tell it that you’ve added paper. I’ve got an “all-in-one” that if it runs out of paper, I can put in more, but then I also have to press the Enter button to resume the job, or it will just sit there blinking “paper out” all day long.
I yell at it. It doesn’t work, but it does make me feel better.
I have this problem a lot less now that I have a printer with paper trays, instead of feeding the paper into the top of the printer.