Here is what happened. I went to administrator tools > Computer management > Local users and groups > Users. Now I double clicked on the main user account. Then I switched to the 'member of' tab. I deleted the things whatever present over there. Then I restarted the system. Now I can only see Guest account. My main account is not visible there to login. I have no other account except Guest account. So I logged into the same but I cannot re enable the main account from here. Or I cannot create any new account from here. But it seems I have the built in administrator account enabled. Screenshot attached. I tried to restore my system. To do so it asked for the password of this administrator password. But I did not set any administrator password. So I'm stuck here with a Guest account. Please help me. By the way my main account is not deleted permanently. Screenshot attached for the same. The same question I posted on some other site: xda-developers dot com showthread dot php?t=1920566
Like I said it asked for me for a password to enter into the admin account. I tried many passwords yesterday. But no success. Today I tried to enter into it without typing any password and to my surprise it let me in. I never guessed it would be like this. I restored my system and everything is fine now. Problem solved.
That's exactly what I was going to suggest. If you don't have a password, try it without a password. Glad you figured it out and it worked for you!