iphone 3g white screen

My iphone screen got destroyed and I bought a new one to replace it. The phone still worked but the crack was not good looking.
I installed the screen but I wasn't careful enough of doing that because now when I'm starting the Iphone my screen shows white screen of death. The first time when I started the phone it worked well but there were some flickering and touch screen didn't worked. A moment later the screen went white. Is there anyway to do some tests to see if my lcd or screen is broken?

Should the lcd screen always show white even if you haven't plugged cable 2 and 3 in?