laptop hooked up to led monitor

[R22000]

I have a samsung led monitor that i have hooked up to my laptop through either vga or hdmi and neither will show up. i usually run windows on it and it works fine and will display it fine there. i am just wondering if i just need to change a setting or something to go to the led screen that i have here. thanks very much for any advice. i am starting to really like sabayon with its rolling release ideal.

[Fitzcarraldo]

Any error messages in /var/log/Xorg.0.log file?
What DE are you using?
What is your GPU?
What driver are you using?
How are you selecting the external monitor? Using amdcccle if you have an AMD ATI GPU and the closed-source driver? Using nvidia-settings if you have an NVIDIA GPU and the closed-source driver?
Have you tried using the xrandr command?