I used the Disk Utility and I deleted the OS partition, because I lost the admin password and I couldn't install anything (my first question). I got an advice about deleting the partition from disk utility. I did it and now I have 2 new partitions.
I had macOS Sierra before. When I try to install macOS now, I get option to install OS X Lion. (I didn't install macOS Sierra myself. I just bought that old macbook one week ago and macOS Sierra was installed.)
When I connect to WiFi to install OS X Lion, I get an error after 10 minutes. I can't install the OS and it tells me that I have to contact AppleCare Support. I don't have an Apple ID. How can I solve this problem now?
How can I install OS X using USB?
I tried to download macOS Sierra and install it via USB but I couldn't open the Apple website from my other Windows laptop. I got an error that the website can only be opened with an apple device. The problem is, my mac has no operating system at the moment and I can't login into their App Store to download the OS.
Any help will be appreciated.
the Core problem was on my internet connection. I connected my laptop to EDUROAM (Public guest internet network) via Hotspot using my windows laptop. After begigning of installation (10 minutes) the internet connection droped to hotspot and this why I got the error. I couldn`t connect with my MacBook Pro directly to EDUROAM because I need to logging to network via HTTP and apple doesnt provide this option by installation :( I solved this problem by using an other internet connexion which is connected directly to router without login.