First, remove the right cover of your printer. When starting up the printer you should see a flickering light (white light), best seen at the right side of the printer. If you cannot see this light, this means your drum and preheater are not heating up, because of no light activity.
To remove the drum heater:
Remove both left an right cover. Remove front door + maintenance drawer. Remove both blue of green plastic rails that guide the maintenance tray. Remove the middle transfer rolls (first, remove clutch on the left side, remove one screw and a little metal piece on the left side of the bar close to the left side, it prevents the bar from moving left and right), then remove these rolls. At this time, you will see the back of the drum heater. Remove two screws and a power-cable on the right side. Be carefull, it slides very easily down. So, if still any problems, don't hesitate to ask...