HOW DO YOU TURN OFF TWO-SIDED OUTPUT ON A XEROX 3325/DNI

https://www.office.xerox.com/en-lb/multifunction-printers/workcentre-3315-3325/supplies

1. If printing in the computer , select Printing Preferences in the computer choosing Xerox 3315 as the printer then choose single sided setting, Apply and OK. that should change the default setting for your computer.

Probably trying to print a job which is set to other then A4

NO NO NO.

Don't rush things. If you don't know how a laser printer functions, please don't touch anything. Let someone with knowledge clean the machine. Rubbing the wrong roller, can damage the printer bend repair.

Only clean the parts you are allowed to clean. Like removing dust on places outside the printing area.

User Manual

http://www.support.xerox.com/support/workcentre-3315-3325/documentation/enus.html

Their is no fax board in the machine

Try new driver and check details; http://ftp.xerox.com/support/workcentre-3315-3325/downloads/enus.html?operatingSystem=win7x64

Xerox Phaser 8400 does not support double sided prints. You have to have a Duplex Unit for Phaser 8400 part number 097S03177 to be able to print double sided. If you have the duplex unit, on the Print dialog box just click Preferences and under 2-Sided Printing select 2-Sided Print then Apply.

You just select 2-sided printing in the print dialog box. I think it's on the finishing tab. I'm assuming you aren't trying to print on 2nd side of pre-printed stock. That would be a different issue.

What driver did you download? The PS driver is much less capable and I am wondering if thats what you downloaded.
I am using the PCL driver and the selections are 1 sided, 2 sided long edge , 2 sided short edge.
Unless you are runnung CAD, you really should be running a PCL driver.
Maybe I am misunderstand what you are telling me also.
If you have the PCL driver and thats still a problem let me know and I will forward all I can find.