I have upgrade the router, then restart it , but not it is struck on loading kernel step. 
i can not reset it, or do anything.
is any way to restore the 5.25 os.
have use the netinstall but no luck at all.
anyone please help!!
We did have the same problem after updating to OS v6.1 and it completely locked down the router - telnet did not work, winbox did not work either… By the way it is a brand new router. 
The only way to get back to its ‘brain’ - we had to press ‘factory reset’ button at the back of the box. It is accessible again and it is still running OS v6.1 but we cannot trust it and sent back to the reseller. 