I can't switch on the GPS

I have a garmin that is used little so when I want to use it it is dead and will not turn on. However when I use the charg cord in my vehicle with the engine running I wait for a few minutes holding the start it will start up. Not just a simple press of the button but hold it. I also try to turn it on when pluged into my computer usb port. it will be on the computer for an hour and still not turn on. But after charging on the vehicle I then can plug into the computer and it works to enter updates. It is an older one so the battery is down hill, needs replacing.

Give this a try, when driving I leave it pluged in always. I have never just walked around to see how long the internal battery will keep it on.