FUSER DOOR IS OPEN CLOSE IT - Samsung SCX-5635FN All-In-One Laser Printer

A notch or little pin on one of the door (trays) that must fitting against a microswitch or a simple brass-blade contact under the hood of the tray or door or sometimes even by a ldr light detecting resistor.

Try fuser door should be in the back. If it is close, it could be a door sensor issue. Also make sure that the fuser is in correctly.

Reinstall software. You do not have to
uninstall the original software, re instalation will roll over it.
Brad

The fuser door is at the back of the machine. Open the door, pull down and close firmly shut. If the error persists it could be that the sensor has gone bad. The sensor is actually hard wired to the High Voltage Power Supply that sits right above the paper tray underneath the machine. It would need to be replaced if closing door doesn't fix the error, the part number is 105N02120,a link to picture of the part is 105N02120 Xerox 3300MFP HVPS Item Inc

Fuser Door Open is the message on the display when it's powered on. I took the back apart, removed the fuser, looked all over. I couldn't see any kind of sensor, optical or mechanical that makes when the door is closed. There's an access plate with a blue latch below the fuser that makes an optical sensor and a mechanical sensor, but that seemed to be OK. It didn't seem like something that would be called a fuser door. So, I pushed on it where it made the mechanical switch and the printer hummed to life and the message went away. I took the fuser out and examined it. The metal brackets where the pivot parts were, seemed a little bent. I straightened them out, stuck it back in and that fixed it.
By moe who hasDell MFP 1850DN this might also help...
or Fuser Door Open
1. Make Sure the Paper Tray is Loaded Correctly With no Obstructions
2. Clear the Paper Jam in Tray 1 or 2
3. Clear the Paper Jam in the Multi-purpose Tray

That is a problem with the fuser door switch which is a part of the High voltage power supply. Replacing the HVPS should fix this right up.

Your problem: paper is jammed in the back of the printer around/in the fuser.

The Users Manual for your printer is located at:
http://www.brother-usa.com/ModelDocuments/Consumer/Users Manual/UM_DCP_7030_7040_EN_1510.PDF

You'll need Adobe Acrobat Reader (free from www.adobe.com) to view it.
LOCATION:The fuser cover is located in the back - its covered by the panel in the back called
the "back cover" aka "back output tray cover".
2-step fix:
(A) open the back cover - on the back of the printer.
HOW: it flips down
(B) open the fuser cover and remove paper jam
How: Pull the 2 tabs (one left and one right) toward you to open the fuser cover.
(it also flips down to open).
Most of this fix comes from downloading the Users Manual and blowing up page 60 (of 108 pages).

There is a black sensor that detects when the fuser door is closed, and an actuator that the sensor either sees or doesn't see. If this sensor is dirty, it might not be seeing the actuator. It could also be broken or knocked out of place.

Locate the actuator on the side door (a small metal or plastic tab that sticks out from the door) and find the corresponding sensor. Make sure the sensor is in place and not broken or moved, and make sure it's connector is well-seated. If you have a can of compressed air, blow it into the sensor to clear away any dust or dirt.

If you have tried closing the fuser door (rear door) several times and the error continues. You most likely need to replace the High Voltage Power Supply (Part# WH773). Iteminc.com has this part and can ship same day. The sensor which reads if the door is open can go bad and it is part of the HVPS. Good luck!

Your Samsung ML-3561ND looks to be an HP Laserjet 4000-series printer. Same engine, different electronic. The fuser is in the rear of the machine, and may be relating to the drop-down rear panel where you clear paper jams. Open it and give it a good push closed and the printer should cycle and come ready. Let me know what happens!