Make sure the fuser is seated and check to see if the fuser rollers turn. Does the paper get crumpled on the leading edge? Does the paper show print? If the paper shows printing then the toner cartridge is OK, if it doesn't show printing then pull the toner cartridge out and open the flap and see if there is an image printed on it; if it is blank then the toner cartridge could be defective or the gear assembly driving the toner cartridge has failed. If the leading edge is crumpled, this will point to the location where the paper is jamming, look for bits of paper in the area where the leading edge is crumpled. If the paper is not crumpled, then check the sensor flags leading into the fuser.