You could first try a simple reset. If that doesn't help, follow this:
Info from here:
All settings, user data*, and satellite data may be erased when resetting the GPS. User data can be backed up to the computer. For assistance, see the FAQ article "How do I back up user data from my outdoor GPS with a USB interface?" before performing the reset.
To perform the master reset:
- Turn off the Astro
- Press Map, Enter and Power simultaneously
- Wait for Astro to power on
- Release Power
- Wait for the message Do you really want to erase all user data?
- Release remaining buttons
- Select Yes
Astro 220 or 320 is now reset. Leave the device outside with a clear view of the sky for a minimum of 20 minutes to acquire satellite data.
*User data consists of waypoints, routes, tracks, and geocaches
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