Check your resolution. Especially if you have a letterbox (square) monitor and a widescreen display on the laptop, or the other way around even. You need to make sure that the monitor supports the resolution you're trying to get it to run.
I thought setting up an external monitor with most laptops was plug and play type of stuff. However, I am unable to get a lenovo x300 to recognize a monitor that works just fine with other laptops.
I believe I have set up everything properly. However, when a toggle I get only a black screen on the external monitor. It does sporadically flash a message that that indicates "1 Analog Input Cannot display video in this mode".
Your help appreciated