ePo "admin" is the user which has " global administrator premissions", so if you are being asked for credentials during installation. it is OK. you may provide any password of your own choice with user "admin" which is default.
I changed the login from Windows authentication to SQL authentication. I used EPOAdmin and its password. When I was presented with the Global Administrator login, I used just admin and the same password and it finally worked. Thank you for your help.