iphone not appearing in My Computer

Look at Device Manger

Click Start, type Device Manager in the Start Search box, and then press ENTER
Click Continue. The Device Manager Dialog box is displayed. If you are prompted for an administrator password or for a confirmation, type the password, or click Continue
In the list of device types, click the type of device, and then locate the specific device that is not functioning.

My iPhone showed under Portable Devices

If an exclamation point appears next to the name of the device that is not functioning, Device Manager cannot find the device driver.
Right click on the iPhone and 'uninstall'
Unplug the iPhone from the USB and plug it back in

Voila, it reappears in Window Explorer