Some questions to answer:
1. Have you powered the device off and back on?
2. When was the last time the device worked?
3. If the device has WiFi support does it work on WiFi but not when its away from WiFi?
4. to the best of your knowledge has anything on the device changed recently, including system updates?
5. This last one may seem silly, but might your wireless service have been terminated for non-payment?