Watch keeps shutting down

Hi,

just got a Garmin 245 as a present and set it up yesterday ( paired it with my phone etc). I charged it to use today and when I turned it on I had 100% battery. However, the watch keeps turning itself off instantly when I start it up. Sometimes it takes a while before it will turn on and when it does it comes up with a message “set up assistance using garmin connect mobile” then turns off. I have removed the watch from my paired devices on my phone and the watch physically won’t stay on long enough for me to try and pair with my phone again. 

any help would be appreciated 

thanks, John