This seems to take a long time (60 seconds at least). Once the pre boot mode message disappears release the power button and your device will perform some activities to recover from the above problem.
Apparently this sequence will only work with the above error.
I assume you have used the bluetooth in those two weeks. All they do is transmit a signal with their id, and the time the signal left the satellite.
I did this as I read some other comments that the Garmin webupdater application has (in some cases) caused corruption.
All of this and they already have an update function built into the unit (Webupdater).