Garmin has an app called "Garmin Express" that downloads and applies the latest version to a GPS connected by USB. It is available for Mac and Windows.
That said, a 'hard reset' by peeling the sticker off the front of the device and hitting the reset button should restore it to factory defaults, at which point it should function again, and then you can try the latest firmware and maps.
Now, that said, this model is discontinued, and the newer models have revised (better) user interfaces, faster processors, etc., so that's "plan B."