When I use my laptop in my office I connect it to a monitor so I can work on two screens. All of a sudden it's not picking up my monitor. Although, my monitor works fine when connected to another computer and my laptop will work with another monitor when I plug it in. Does anyone have any idea what the problem is?
I've had similar strange behavior on my laptop/monitor. For me, rebooting the laptop is the best fix. Sometimes if you right click on an empty spot on your desktop and click properties and then settings you should have an "extend my windows desktop onto this monitor" checkbox. If it's greyed out, and you see a big "1" and big "2" then click on the "2" that's your secondary monitor. The message above should become black again and you can check the box.
If you have a "third party" monitor management application, all bets are off. You can also try (function button) fn and F8 from the laptop. Give it a couple seconds to refresh- then again in it switches to the monitor completely. Usually that replicated the monitor- it doesn't extend the desktop.