No network since I changed my display

Since I changed my broken glass/display on my Iphone4 using ifixit repair guide.

My Iphone is searching networks for hours, sometimes it find my prvider (vodafone germany) and I get just one bar.

If I move the phone, it instandly loses the connection.

The Phone is free/unlocked and the sim card works fine in every other phone/Iphone I tried!!

Also, I had a small plastic/rubber thing left over after I finished changing the display, couldn´t found this little part on any of the Iphone4 pics over here

any advise??

Thanxs, Dan