If your Nexus 7 fails to rotate (or any other Android device), here are some solutions to see if you can correct the problem.
1. Access the Notification Bar
2. Look for a Lock Symbol icon
3. Click once on Lock Symbol icon
4. Rotate the Nexus 7 device
Your Nexus 7 screen should start to rotate but keep in mind that some apps will not operate in Landscape mode and will only be shown on Portrait mode.