HELP! (Screen detecting problem)

Hi everyone!

I really need help.
When i plug my Macbook Pro to my external screen (Dell 24"), there is just coming a blue screen up on the computer, then it goes away, and notting happens... =My lovely Macbook does not connect!
It is very frustrating, because it used to work. It is not the DVI adapter, because sometimes it works, but now lately, it almost never works.
I have also connected it to a projector, and there is the same problem... =It's not the DELL external screen.

Guys... Help me!!!

 

Help!

I don't know what that software is doing. I downloaded it, but there it is just saying something about, that my computer don't have dual core. Mine is from 2010.
Is there overall any software, which can help me???

Thanks for the response!