What to do when your printer is not printing, easily follow this step by step list on troubleshooting you printer problems.
Check the power on the printer;
make sure the printer has power and that there is a light lid up on the printer, saying that the printer has power.
Many times we accidentally kick or step over a power cord making it came loose, losing its connection.
Check the cable connection between the printer and the computer, (USB or Parallel cable)
Again kicking and moving the cables under the desk can make a device not function properly.
If USB printer, check that the USB cord in the printer end is connected to the USB connector.
When we have printers that have network connections, it is really easy to connect the USB cable in the RJ-45 (network) connection, especially when the two connectors are side by side.
Check the printer itself, make sure that there are no blinking lights
If we have blinking lights it means that there is something going on with the printer, maybe when we remove the paper jam on the back, we forgot to check the front side of the printer, many times there could be a paper jammed next to the print head.
Check the status of the printer on the computer, by going to Start menu –Control Panel- Printers and Faxes. 
In the example image above we can see that the HP DeskJet 3420 series printer is offline, meaning that the printer is unplugged or powered off.
Your printer should always say online, when working correctly.
This can also mean that there is an issue with the drivers, reinstalling the drivers should fix the problem.
