This may sound silly but have you tried different sorts of media through the printer, or even more importantly, have you checked the paper type settings on the printers front control panel, either could cause loose toner even after replacing a fuser.

If you haven't already, you should remove the RAM, and reseat/replace one module at a time. Faulty RAM or a faulty RAM slot can cause no video display. You don't always get a beep code to tell you this.