My FN+F6 doesnt keep my screen on the laptop open

You sure it's not that you just haven't switched over to getting the screen to display on your external monitor, not just on the laptop? It's usually done by pressing the Fn key (bottom-left on keyboard), and a function key (eg F5/F6).

You can switch to an external monitor or data projector by two methods. 1. Connect the external monitor to the laptop's video port, power up the external monitor first and the laptop. The video information will automatically switch to the external monitor. 2. If you power up the laptop first then you can switch the video output to the external monitor by pressing the Fn key and one of the Function keys, depending upon your make and model laptop. You can also toggle between the external monitor or both LCD screen plus the external monitor or back to LCD screen only by pressing the Fn key plus one of the function key. Here is a list of key combinations for some of the laptops :- IBM ThinkPad = Fn + F7 HP and Compaq = Fn + F4 Toshiba = Fn + F5 Dell = Fn + F8

The following applies to Acer Laptops. You did not specify the brand of laptop you had. If your laptop is not Acer, the specific keys mentioned may be different and you should adjust accordingly.

If the power indicator is lit but nothing appears on the screen - The computer's power management system automatically blanks the screen to save power. Press any key to turn the display on.
If pressing any key does not turn the display back on, check the following....
1. The brightness level might be too low. Press Fn and the right cursor key to increase brightness level
2. Display device might be set to an external monitor. Press Fn and F5 to toggle to the internal display
3. Backlight might be turned off. Press Fn and F6 to turn on the backlight.
4. If the Sleep indicator is lit, the computer is in Sleep mode. Press & release power button to resume.

you need to setup your laptop display to clone mode.
you can also look for the FN key and the two LCD's button which could be f6 -f8
press on that until your display switches to clone mode.

Hello,

Try this

Function Keys Fn+F1 - Places the computer into sleep mode
Fn+F2 - Changes the (I-Powerxross) power settings
Fn+F3 - Switches display modes: LCD only, External monitor only, LCD+External Monitor
Fn+F4 - Turns Wireless LAN on/off
Fn+F5 - Switches OSD (on screen display) on/off
Fn+F6 - Turns the Touchpad on/off
Fn+F7 - Turns the Webcam on/off
Fn+F8 - Mute Sound
Fn+F9 - Reduces speaker volume
Fn+F10 - Increases speaker volume
Fn+F11 - Reduces the screen brightness
Fn+F12 - Increases the screen brightness
Fn+Esc - Toggles Bluetooth & 3G on/off (optional)

Thanks

Fn + F5 toggles the display output, the trick here to wait each time you hit this combination because it goes through several options. Hit it once and it may want to go to just the external, then both the laptop screen and the external. etc. Now Fn + F6 turns the backlight bulb off on the internal monitor to save energy. Now I am giving up the link to your service manual, it is in PDF format so you can make a copy for yourself and keep on the laptop, print it or save it to a flash so you can reference it later. I believe if you take the keyboard off and disconnect the video lead on the left side where the display plugs into the motherboard, then when you power the laptop back up it will default to the external cord and you can use the laptop without any switching. That is what I am doing with an Aspire 5920 that I am rebuilding. Good luck, ParrotHead PC Repair
Just copy and paste the link below to you internet address bar and hit enter.

http://tim.id.au/laptops/acer/aspire%203680%205570%205580.pdf

A quick test would be to connect it to an external monitor.

Also try the FN+F5 or FN+F6 keys with and without an external monitor connected.

If you display come back using the keys it was probably just an accidental key press

If you can get an external display but not a laptop one then there is an issue with the display or the graphics card section of your laptop and further investigation would be needed

It could be the 'back light' is burned out.
Or
Press Fn and F5 simultaneously to make sure the display
priority is not set for the built-in screen.
Or
Press the 'brightness up' key a few times.

Display problems
Here are some typical display problems and their solutions:
The screen is blank.
Display Auto Off may have gone into effect. Press any key to
activate the screen.
You may have activated the instant password feature by pressing
Fn and F1 simultaneously. If you have registered a password, press
any key, type the password and press Enter. If no password is
registered, press any key. The screen reactivates and allows you to
continue working.
If you are using the built-in screen, make sure the display priority is
not set for an external monitor. To do this, press Fn and F5
simultaneously (once). If this does not correct the problem, press Fn
and F5 simultaneously again to return the display priority to its
previous setting.
HINT: Holding the Fn key and pressing the F5 key several times will
advance you through the display options.
If you are using an external monitor:
❖ Check that the monitor is turned on.
❖ Check that the monitor’s power cord/cable is firmly plugged in.
-- Try adjusting the contrast and brightness controls on the
external monitor

Change the settings from the display settings panel. (Right click on the desktop and go to display settings)
You should see 2 monitors graphically represented there. 
You can make the monitor that is greyed out active by right clicking on the monitor, and selecting active.

does it work with external monitor ?
the key should be Fn+F5 or Fn+F6
I believe you need to hold fn and press f5 to choose the target (lcd, monitor, lcd and monitor).