My heart just about stopped today when I went to use my Garmin 305 and it was completely dead. I tried a couple of different chargers and it wouldn't come to life. I went on a bike ride without it hoping it just needed to charge for awhile.
It still wasn't working an hour later. Luckily I found this tip on the gamin website:
You have to hold down the "reset" and "mode" buttons simultaneously then push the on/off button while holding them. It powered right up and all is right in the world again!