An administrator password in Windows 7 is the password to any account that's setup to access administrator level functions in Windows 7.
There is also an account called "Administrator" but it's disabled in Windows 7 by default. What you really need in most cases is the password to any account that can act as an administrator.
There are a few times when you will need this password. You may need an administrator password in Windows 7 if you're trying to run certain types of programs or access certain Windows 7 recovery tools.
Follow the steps below to quickly find an administrator password in Windows 7:
Try leaving the password blank if you're trying to log on to the actual "Administrator" account. Just press Enter without typing anything when asked for it.
This trick doesn't work nearly as often in Windows 7 as it did in Windows XP but it's still worth a shot.
Enter the password to your account. Often times, depending on how Windows 7 was setup on your computer, the primary user account will be configured with administrator privileges.
Try to remember your administrator password. As I mentioned in the last step, your account might be configured as an administrator, especially if you installed Windows 7 on your computer yourself.
If that's true, but you've forgotten your password, you might be able to make really good guesses at what the administrator password might be.
Have another user enter his or her credentials. If there are other users that have accounts on your Windows 7 computer, one of them may be setup with administrator access.
If this is true, have the other user designate you as an administrator as well.
Recover an administrator password using a Windows password recovery tool. You may be able to recover or reset an administrator password with one of these free tools.
Note: Some password recovery tools in the list I linked to above also have the ability to add administrator privileges to regular Windows 7 user accounts which could be valuable if you know your account's password but it's not an administrator account. Some can also enable accounts like the "Administrator" account.
Perform a clean install of Windows 7. This type of installation will completely remove Windows 7 from your PC and install it again from scratch.
Obviously don't attempt this extreme solution unless you absolutely must. For example, if you're needing an admin password to access operating system diagnostic tools and this is your last effort to save your PC, performing a clean install will work because you'll have an opportunity to setup a new account from scratch during Windows 7 setup.
Looking for your administrator password but you don't have Windows 7? See How To Find Windows Administrator Passwords for instructions tailored for other Windows operating systems.