nds lite wont turn on after screen change?

Hi i go the job of changing the case on my nephews ds lite as he broke the right hand hinge(like usual),so i bought a new case and took it apart using the right tools and following a youtube totorial but also managed to tear a litle bit on the top screen flexy ribbon wires trying to get it through the hinge hole so i had to then buy a new top screen erghhhhhh and i got a new hinge for it to as the old had lost its locking properties.so i put it all back together carefully and it has the same fault as it had with the broken hinge,the power light will come on (green light) for about 1-2 seconds and then goes off.i also hear a feint crackle from the right hand speaker and you can just see a feint flash from the botom screen but very feint it needs to be dark to see i.does anyone have any pointers as to what could be wrong with is as i am supposed to be fixing it for xmas !looks like i may have to get him a secondhand one.thanks in advance .adam