Already checked the community, maybe due to my bad keywords or the search engine, I was not able to find the right troubleshooting steps.
i got everything mentioned in Raspberry Pi - Home Assistant and was able to install and access the HA running in the default instance as mentioned in the Onboarding Home Assistant - Home Assistant . i was experimenting something and I thought lets restart, I was unable to access the URL from that time. I couldn’t find why it happened so I re installed everything from scratch. It was working fine.
i dint make any changes, I restarted again, from that moment , I’m unable to access to URL.
Why is it happening? and how can I prevent it from next time?
That really depends on what you have configured since you installed it.
Also are you using the developer options to restart it. If so, that will tell you what is wrong if you check configuration before restarting. HA will not let a restart happen if the configuration is faulty if you restart it via developer options. Any other way of restarting is open to risks not worth taking.
Config check happens at EVERY HA restart since sometime early last year.
Is it on the network? (can you ping the IP address)
Can you reach it in a browser by Ip address
Is the box on? If so what’s the console say? (hdmi to a monitor of youre running headless)