How is your printer connected to your computer? If it's wirelessly, then it seems likely that it's lost the information that tells it your router's SSID and Security Key.
Otherwise it could be a fault with the printer driver.
Either way, a 'clean install' of the software that came with printer will probably fix the problem. Go to your 'Printers & Faxes' folder (from the Control Panel), right-click on the icon for your printer and select 'Remove'. Then run the set-up software for your printer again.