When the HP Deskjet 940C encounters a problem, it turns on its trouble lights to alert the user to the issue. When the problem is resolved, those trouble lights should turn off automatically, allowing the printer to function normally again. However, at times the process does not work as intended, and in order to turn off the trouble lights and resume printing, printer users need to perform a reset on the printer. Performing the reset procedure is necessary if the trouble lights on the 940C continue to flash even after the underlying problem has been resolved.
Power on the printer and open the top cover. Wait for the print cartridges to move to the middle. Remove both cartridges and set them aside.
Shut down the printer and remove the power cord. Leave the printer off for one minute.
Plug the power cord in but do not press the "Power" button on the printer. Reinsert both of the print cartridges.
Press the "Power" button to restart the printer. The lights should now be reset.