I tried all these and other website suggestions. Laptop wouldn't recognize or charge my iphone 6. Laptop wouldn't even say an iphone was attached to the laptop.
This simple trick worked for me. I plugged the cord to my Iphone and then connected to the computer - same results. I then unplugged the Iphone only and plugged it back in. Then my laptop saw the Iphone and I went to ITunes and it asked to allow Iphone to sync.
Don't ask me how, but this worked in my situation.