IPhone 3G black screen

I replaced my faulty LCD on my iPhone 3G this morning. When I put in the new LCD and turned the phone on the display looked a bit dim and faded, so I unhooked cable 1, 2&3 with the phone still on then reconnected the cables. Now the screen isn't turning on at all, the phone is on because it vibrates and makes noises, but the screen is just black. I had a look on google and I think the problem is that I unhooked and reconnected the cables with the phone on, apparently the phone should be off before you fiddle about with it. I've tried removing the motherboard and restoring the phone on iTunes, but the screen remains black. Any help would be greatly appreciated.

I'm not 100% sure but turn off the phone again and try unhooking the cables, then reconnecting them.