win 7 is no longer supported by Microsoft so their drivers develop bugs
go the the Panasonic web site , find your model printer and the download compatible with win 7 and download and run from there
Press Menu first, then #9000*, next press 550, press Start, wait for printing, unplug the electric cord, wait 10 seconds or more, plug it again - sorted.
First of all replace the toner cartridge, if it doesn't clear, check the developer unit for any gear wornout and rectify. This should solve your problem, good luck!