Switch to your core database and execute the SQL below to reset the password to b:

UPDATE [aspnet_Membership] SET Password=’qOvF8m8F2IcWMvfOBjJYHmfLABc=’
WHERE UserId IN (SELECT UserId FROM [aspnet_Users] WHERE UserName = ‘sitecore\Admin’)
Alternatively navigate to /sitecore/admin/unlock_admin.aspx and click Unlock Administrator. For this to work, you must first “unlock” the functionality. Open up the .aspx file and modify the following code:

// TODO: to enable the page, set enableUnlockButton = true;
private bool enableUnlockButton = false;