When you try to login Joomla it might just return the login screen without any error message but not logged in. You can try to follow the steps below to get it resolved:
1). connect to your mysql database via phpmyadmin,
2). go to the table jos_plugins.
3). Then scroll down to User – Joomla!
4). Click on the Edit icon
5). Go to the area where it says published and change that from 0 to 1
Now try to login again and it should work.