How do i connect a external screen as main?

Hello, I have a samsug notebook that my dad gave to me like last year and the screen isnt broken but it's really dodgey as in it'll flicker and go black or white or the picture will go completely, and i have to hold to bottome left hand corner to make the screen ok again as you can imagine this causes major cramp in your thumb after a while so i decided to connect a old screen when i first plugged it in it worked fine, it was just my desktop on the other screen as well as on my netbook all hunky dory happy days. I unplugged it because i was taking my netbook downstairs for somthing, and when i plugged it back in the external screen didnt come on it just stayed blank. After playing around with the settings i managed to get my notebook to extend my desktop to the external screen and is nice, but not what i wanted i just wanted it the way it was before where my entire desktop was on the external screen as it is i dont even have a start bar on the external screen. It works fine for now i guess if i want to work on the external screen i can just drag stuff over too it. But i figure it's just a matter of time before my netbook screen bites the dust so dose anyone have any ideas on how i can maby get it back to how it was? if anyone needs anymore info i can take screenshots but i'm not exactly computer wise so if you just talk to me in computer lingo i wont understand what your saying haha

~ A confused teenager <3