WLAN does not connect to a network

Hi guys, just found your wonderful site and hope anyone can help me out here in Germany. As usual guarantee is over and electronic gadgets fail, so in my case here in Germany. My iPhone 4 is not able to connect to a wlan network anymore. We did everything in my company in between software and hardware reboot... The network is always trying to connect to a wlan, from time to time it finds one but you can not choose anything and then same procedere in searching a wlan. So what can I do here or in other words what is broken here and can be fixed ?

Help would be appreciated befor I go to a shop and have to pay a very expensive repair while perhaps with your parts I can fix it myself ?

Hope someone can help me out.

Regards Sandro