My xerox phaser has a blank screen and no green light on the front of printer. I can hear the fan so I know it is getting power...... also when I plug the usb into my computer, my laptop reads that the printer is off-line. It does not recognize the printer. My printer has less than 10,000 copies so far. I replaced a heater bulb last year but I have never had a problem until now.

Wendy, Please where did you get the heater bulbs? It seems i need some. My xerox phaser 7800 do not power on, fan and gears do not turn when you switch on only green led light on and the screen is off.

That sounds like one of two things.
Either the ribbon cable to the screen needs reset, you have to remove 4 screws I believe it is, then unplug everything to that assembly, and re plug them back in.
If that does not repair it, then most likely the electronics module has failed. That is quite expensive to replace.