If you are using the blue VGA port then try shutting down the machine, Ower on the projector and set it to VGA input and boot the laptop.
Then see if you get a response as the machine boots.
Once you are all the way into windows then go to your display settings under ctrl anel and se if the projector shows in advaned.
Let me know what happens.
First click the FN+F2 3 or 4 pausing for 3-5 seconds between presses, I am not sure which one it is on your Dell, Just look forthe key with a picture of two monitors with a / in between.
Then go to the advanced settings under display and see if both monitors show if they do then decide if you wish to extend your desktop so you have dual monitor setup or leave alone and set it to duplicate so you get the same view on both monitors.
Let me know what happens and also your model number so I can get you the correct kwy combination.
Give me the model of projector.
Did you get the dual display to work with the FN+ F3 key?
Let me know
So let me get this straight, You can use one display or the other not both at the same time.
Does everything else work on the laptop when you use the external projector?
Well I made a mistake it is meant to be FN+F8 (I called one of my techs who has a Dell)
Try that and I will let you know about the control keys on the Projector.
When you installed the projector and its drivers did you also connect the USB cable?
Did windows recognise it as an input device?
There should have been a usb connector from the projector to the Laptop so that it can control the page up/down keys.
What is the precise model number of the projector, Is it the LP240? http://www.infocus.com/Support/Products/Projectors/LP240.aspx
What operating system and service pack do you have?
So you have to purchase the cable for your keys to work?
So cycling with the FN+F8 does nothing?
Disconnect the projector and reboot your laptop then connect the projector.
Go to displays then advanced and see if two monitors show in the advanced tab, If they do then select clone.
If not thell me what version of graphics driver you are using.