Hello. Something strange is happening to me. I suddenly can’t access a specific URL. A week ago, I could… I haven’t changed anything on the Mirkotik router…
It has nothing to do with the router.
So what is it?.. because if I use a network outside the MikroTik I can access
For starters, you gave us almost zero useful information. Is this a URL on your LAN, something out there on the web, something else???
Well it was a little better than “there was no sugar in my coffee”, as at least we know equipment that accesses the www was involved, unless it was a bad dream! 
its a url in the web i think they block me
Some admins like me are mean you try to probe stuff they give you a 1 to 3 day blacklist. Did the block occur after you tried to probe something?
If it is a blacklist it will drop of in a couple of days.