404 when I open admin-panel

Hi,
the installation of "grav-admin" is ok, when i digit: http://www.mysite.xx/grav-admin it says - Grav is running!

But when I digit: http://www.mysite.xx/grav-admin/admin for enter in admin-panel, it says "error 404" :-(

Please, help!
Thanks

Might any of this info help? https://learn.getgrav.org/troubleshooting

Thanks for your advice, but I am in difficult.
Where are "AllowOverride", "httpd.conf" or "apache.conf"?
My GRAV is on a Windows server.

Thanks