iPhone 6 won't connect to Windows 7
Go to Control Panel / System and Security / System.
In the System window check the System type for wether your operating system is 32-bit or 64 bit type.
Make sure your iTunes is 32 or 64 bit as per your operating system.


If this is ok then - 


Type services.msc and click Ok.
Make sure Apple Mobile Device Services is set to Automatic.


If this is ok then - 
I would suggest you search - "Apple Mobile Device Driver" and install them.