A sun fire 480 server because ping-able but not accessible , when we gave up , we restarted the server and everything is fine and the server is accessible. I'm couldn't get an explanation for what happened.
It will be impossible for anyone in the forum to help you to find a root cause.
No one has remote access to the system (and is not EVER going to get such access because that would be a flagrant security flaw), so no one can examine any system logs for details you accidentally missed.
You didn't provide any excerpts to any of your log files, nor any extensive description of that system in your data center (connectivity, assigned usage, or anything else relevant), so it would require mental telepathy to investigate the system.
You have an Explorer file.
Go log a SR with Oracle TechSupport and have them examine that file.
If you cannot do that, then just make note on the calendar that the event occurred and go on with your business as usual.