I wanted to use power point on my tosbhiba lap top ,with the benq projector.i hooked it up and my montor went black but i can still the program on the projector screen what now?

You were succesful

Now run the powerpoint presentation as you would on a normal screen.

Most laptops also have the ability to run both displays at once and you may want to check out that ability too if you are having problems operating on a large display.

I usually use a wireless laser pointer presenter that operates as a mouse so that I can wander while using presentations.