After trying to replace the front glass the iP5 wont turn on?

Hi,

As i cracked my iphone 5 front screen i went to replace it today following this video:

http://www.youtube.com/watch?v=WxSu42ed4aY

In this video i was at 07:40 where you unscrew the screws on the backplate that hold the lcd

But i couldn't unscrew one of the screws on the side of the backplate, it wasn't rounded off i just couldnt unscrew it,

So i put everything back together and screwed everything back, but now the iphon doesnt turn on?!!?

Before i open it back up, does anyone know why it now doesnt turn on?

i didnt touch the battery so i dont get why it doesnt turn on?

thank you