Hello, Sorry you're having problems. Please press and hold the right hand button (labeled "Light") for 10 full seconds and release, then wait a minute and see if the GPS will turn on. Let me know what happens.
If that does not work, then remove the battery cover (slide it off) and remove the batteries. Wait 30 seconds then put the batteries back in and press power once. If it still does not show anything on the display, press and hold the Power/Light button again for 10 full seconds and release, then wait a full minute to see if anything shows up on the screen.
Beyond those steps it would be worth replacing the batteries in the Etrex if you have not done this already.
If you need further assistance let me know. Before you go, PLEASE DO click at least a 3 STAR RATING, at the top of your screen. That is how I am credited for my efforts by the site. You can follow up any time as needed at no additional cost.