Macbook Pro connects an external monitor only after reboot My old 13 inch (2008 or 2009 model one of the first unibody models) macbook works fine in connecting external monitors with my VGA adapter.

My new 15 inch has issues with the same connector. I have to reboot in order for it to work. When I plug the adapter with a cable in the new macbook - nothing happens. When I unplug it, the screen goes to blue and then goes back.

What could be the problem? I think I have this issue from the time I got the laptop. It is with Mountain Lion (it had this issue with all the versions of the os). The old mac is also with Lion.

Could this connector be somewhat different and the new mac to require a new connector?

I reset the NVRAM or whatever, it didn't help
This is the solution:

The 15 inch Macbook uses 2 graphics cards. I use gfxCardStatus application to control which graphics card is used - OS X too easily allows apps to request the more powerful card, which drains the battery too quickly. Skype is an example of such an app.

I just discovered that the integrated graphics card (the weaker one) cannot support a second monitor for some reason. Even though in my 13 inch Macbook it can. So only the "discrete" (or the more powerful) card can do this.

In essence, either stop gfxCardStatus app or go to "Discrete Only" mode in it.