Here is the answer I got from Garmin Support, and it fixed it! 🙂
Problem was that the unit booted with the Garmin logo, showed “Loading Maps”, after that disappeared, it should have shown the Dahsboard, but it just powered off. (before this I had the Garmin lay around for almost 1 1/2 year, not being used)
First make sure the Garmin is powered off. Then press down and hold with your thumb on the right bottom corner area of the Garmin. Continue holding and power on the Garmin. When the Garmin comes to a screen that it seems to be stalled on release your thumb and you should be given the option to erase all the data.
After that, I used Garmin Express to install software and maps again.