Since yesterday, I’ve been having a problem with my Home Assistant Green: it’s no longer accessible on my network. I’ve been using it for about five months, initially with DHCP, and later I assigned it a static IP address via my router. At first, I still seemed to have some connection to it and made some changes to the network settings, but now it’s completely unreachable. How can I fix this?
revert any network settings and so, other wise : After weeks of successful use, unable to connect to HA Green after Reset - #19 by Tolt
If it’s completly unreachable then how do you know it hasn’t crashed?
Step 1. Connect a keyboard and display to the Home Assistant host.
Thanks everyone for your responses. I finally found the time to take a proper look at it. Connected the keyboard and screen and got to work with your tips. I couldn’t really figure out what the issue was, and in the end I tried doing a reinstallation, but that also failed. After that, I took another close look at the network settings, and by adding several DNS addresses the HA Green suddenly had a connection to the outside world again. A mystery to me, but well… it seems to be working again.
Now an other message appears: Unhealthy system: Duplicate Home Assistant OS installation.
So work in progress 
so… assuming your experiments with network setup destroyed your DNS entry.
I think instead of adding ip addresses in your hosts file you should add the DNS entry back again.
Assure that this returnes internal addresses as well - mostly your router will do when you use DHCP on it (of course use your router as DNS )
Regarding duplicate installation - don’t know how you managed that but a fresh installation will get rid of this instead of trying to recover. All the time there is garbage left and a new installation is quick.
Don’t forget to do a backup of your HA