CubeG-5ac60 won't show up in winbox nor netinstall

I have a CubeG and wanted to upgrade firmware from factory 6.48.4 to 7.6. After I did first reboot in didn’t show up in winbox. So I tried a factory reset via reset button. That didn’t help either. So I tried netinstall, but the cube wont show up there either. Any idea what can I do to revive it?

For me the very first answer for https://www.google.com/search?client=firefox-b-d&q=mikrotik+netinstall+not+working gives help https://help.mikrotik.com/docs/pages/viewpage.action?pageId=1409054