To reset your Samsung SCX 3405W printer, you will need to power it off and then unplug the power cord from the wall outlet. Once that is done, press and hold down the Stop/Reset button while plugging the power back in. After a few seconds, release the Stop/Reset button, wait for a few moments until all of its lights turn on indicating that it has been reset. If this doesn't work or if you get an error message when trying to use your printer after resetting it, try powering off once more and repeating these steps again.