No GSM network, low wireless netword

I have a iphone 5 and no have GSM network and yhe wireless network is very low, only close to the router work´s. I open the iphone and verify th one of the two flex are broken. I order the 2 new flex and replace it.

I turn on the iphone again, and dont have network like the first time.

What could be the problem?

What is the job of the flex? broken or not the iphone runs in the sameway!!

Sorry my english.