iPhone 4 no service after repair

Hello, I am Italian and I would get help from your site because it seems to me the best in repair iphone.

I disassembled my iphone to replace the speaker.

after installation I discovered that my signal was always "no service"

I tried to upgrade and restore my iphone several times but without results.

when I am out of the house where the signal is very strong then receive my iphone 3G 2 bars at most.

What should I do? is a hardware problem or software?

please help I'm going crazy without my iphone.