GPS problem

Hi 

I have a problem with my Garmin Edge 830, when I start it there is a message saying that an update of the GPS has been made but when I start my activity nothing happens and the message keeps on showing from time to time. It looks like it has troubles finding it because the clock is also wrong for example I rode this morning at 10am and it said that it was 3am ... 

I tried to update with Garmin Express and I also did a reset but nothing has changed and I still have the same problem. 

Has it already happened to someone ? Do you have any solutions to resolve it ? 

Thanks in advance !