If both the web interface and the Diagnostic Tool are not reachable.
First, don't panic!
Second, check these:
Make sure your hub's IP address didn't change.
Ensure that the device is on the same network (subnet) as your hub.
Check your local network equipment and settings (including Ethernet cable, firewall settings, etc).
Check the hub's LED and if it's red, unplug the hub for 30 seconds before plugging back.
May I add to this tip? Especially don't panic if the Hub's LED is green (C5/C7) or blue (C3/C4). Also, even if a C5/C7 LED is blue, this is still most likely a recoverable situation.
Good point, that reminded me, to add another one, that's rare, but does happen. Check the hub's LED and if it's red, unplug the hub for 30 seconds and then plug it back in. 
What would be on this situation where is a C7 with green lights and no web but only the diagnostic tool responding?
You should try rebooting from the diagnostic tool.
That is typical side-effect of corrupted database. Soft Reset is recommended:
Already done 5 times. Also I did the platform reset and also a hard reset 2 times....
Did around 10 times
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