Thank you for contacting Garmin International.
I will be more than happy to assist today, regarding your Edge 500.
You may need to update your firmware, or perform a master reset for your unit. The former will ensure that your device is functioning correctly, while the latter can ensure that corrupted or damaged files, aren't affecting your unit's operating system.
To update your unit, please see our WebUpdater program found here: http://www8.garmin.com/products/webupdater/howtoinstall.jsp
Please follow these instructions to reset your device:
* Please note that this action will erase all user data, and reset your unit back to default settings.
1. Ensure the device is powered off and disconnected
2. Press and hold the following buttons: LAP + POWER
3. Wait to see the screen that says, "Do you really want to erase all user data No/Yes?"
4. Choose YES.
After the master reset please place your unit outside so that it has a clear view of the sky for 5 to 10 minutes so that the unit can acquire new satellite almanac data.