What windows version are you running? Usually it will prompt you when you plug your phone to the computer.
Import photos and videos from your iPhone, iPad, or iPod touch to your Mac or Windows PC
Before importing your media:
- Unlock your iOS device using your passcode, particularly if you've never synced your device with the computer before. Learn more about iOS passcodes.
- Makes sure your iOS device trusts the computer you want to import your media onto. Learn more about "Trust this Computer."
Windows 8: Learn how to import photos and videos from a camera, phone, or DVD (Windows Help)
Windows 7 and Windows Vista: Learn how to get pictures from your camera to your computer (Windows Help)
If your computer doesn't recognize an attached iPhone, iPad, or iPod touch as a camera, and prevents you from importing photos to your computer, learn how to resolve the issue.