The only thing left to try is a full soft reset.
While everything is on and plugged it, pull the connection cable from the back of the printer. Then pull the power cable. You are going to leave it unplugged for 30 minutes.While it is off, reseat all the ink/toner cartridges and all the paper in the tray.On your computer, uninstall any software for that printer and reboot.After 30 minutes, plug everything back in and turn the printer back on. Hold the power and the print/scan (if you have one) button down for ten seconds.This procedure should clear out everything in the printer buffer. Also, your computer may need to re'find' the printer.If you are still having issues after this, it is likely there is a hardware problem (cable, printer sensor) that is causing it.
I just saw that your OS is Mac. I better opt out, as I am a PC expert.