Ok, I removed that error component not found by adding another menu, choosed type Contacts » Category and made it default. So now it loads when I load localhost/joomla15
So what type should I actually choose for it to be the home menu? I don't understand.
I could reinstall the joomla and see now. But if the project is big, and reinstaling it and putting everything to it from scrathc may take much time, so I want to learn solve problems without reinstaliung.