I had the same problem with my etrex legend and came upon a fix by mistake. I pressed and held the on-off button and the zoom up button at the same time and held for about 30 seconds then I pressed and held the on-off button and the zoom down button at the same time and held for 30 seconds. I don't know which one worked, but now it is working again.
Also, after arriving home a couple hours later, I went into webupdater and updated the software. I don't know if this was necessary, but figured it couldn't hurt. Now my GPS is working like it was new again.
e-mail me at hjmorrison@alltel.net if you try this and it works.
good luck
hermjm