I am with Hamluois, a sytem that requests a password when none existed before and it was not set means that the system is either infected with malware/ransomware or the default account has been corrupted. Assuming that the account is corrupted, this will help (please be SURE that there is no malware or virus first!) You will need to log into the admin account (with Windows 7 this is NOT the default account, however in most cases the administrator account is disabled). If you can get a copy of an ERD for Windows 7 that would be a preferred method up enabling the account, but barring that you might want to look at the instructions posted on sevenforums here: http://www.sevenforums.com/tutorials/102552-built-administrator-enable-winre.html
First, enable and log in as the administrator. Copy all of the users files out of their account (found at c:\users\<username>) without copying the entire account. It is best if you only copy the desktop, documents, favorites, pictures, music, and video folders. Ensure that you have everything that will be needed copied into a folder on a thumb-drive or a folder on the desktop. Then properly delete the user account (right click computer, go to properties, go to advanced system settings, click on settings under user profiles, find and delete the user account). Restart the computer, then create a new user account. Have the user log in, then log out and restart again. Log in with administrator account, copy all of the recovered files back into the users folders. Restart again and the user should be good to go.
Next, create yourself a recovery account to prevent this from happening again. Basically, create an admin account that is NOT the users normal account. Keep it hidden, but enabled. Then disable the built in admin account, as it served it's purpose. If you are unable to do this please find someone who can safely accomplish the tasks safely.
(edit: corrected spelling errors)
Edited by wing987, 10 June 2014 - 02:15 PM.
-- Windows 7 Ultimate on custom built system, Windows 10 on under powered laptop. Sophos UTM 9, Ubuntu Server and Windows Server 2008 R2. HyperV Virtualization --
"The hottest places in hell are reserved for those who in a period of moral crisis maintain their neutrality," John F. Kennedy