iPhone4 wifi connection not working

my iphone4 now no longer connects to the home wifi network or any other wireless network (so all data is provided trough 3G!!)
It picks up the wifi signal (the network is shown with a check/tick mark next to it) but the phone does not connect.
I have forgotten network reset network settings carried out a full restore and reset the phone to factory and still nothing....
When comparing to my girlfriend iPhone4 which has had firmware upgrade as well at the same time (exactly same phone purchased at same time) and yet seems to work no problems there is data missing in the network settings such at router.
Also the iPhone3Gs, MacBook Pro, Compaq etc in the house have no problems.
is it a hardware fault???
Iphone 4 iOS 4 os v4.3.1