closing lid turns off external display?

Hi!

I just plugged my Macbook to my external display for the first time.

I works, if I keep the lid open (with crappy resolution), but if I close it, mac goes to sleep and the display turns off as well.

Well, as I read, this is normal and now I should be able to awake it by pressing any key (on an external keyboard).

But when I do so, the display wakes up only for about 2 seconds and goes black again! What am I missing here?

Thanks!

You can not use an external display in that manner when the computer is on battery. Plug it into the AC mains and the external display will remain on.

Follow these Apple instructions for using your computer in "clam shell mode" with an external display. Link

Regards.

Thanks!

I actually just found the very same answer in another forum post about 2 seconds ago