I had a balance just a while ago but now it shows 0?? Where are they?
Your Nano is safe, no need to worry.
It can be very jarring and cause understandable concern when your balance displays as zero! But rest assured this is expected behavior of some mobile wallets when losing connection to a back-end server.
You will have to wait until the problem is resolved by the service in question. If you need to access your nano immediately, then import your wallet seed into another mobile, web or desktop wallet.