Validating windows 7 ultimate
The most reliable and easy way is, of course, to use one of the provided activators.
You may find yourself in a situation where some activator is not working. Each version needs its own activator, so if you haven’t managed to activate Windows 7 Ultimate for the first time, do not rush to find a working product key, just download another activator file and try again. Using an activator program has many advantages over using a license key.
To do so, click the Start button, type “Activate” into the Start menu, and click the Windows Activation shortcut.
Did you have any trouble re-activating Windows with Microsoft?
The big problem is finding the working license key.
Since after becoming publicly available, the key expires very quickly.
Actually this problem occurs when there is a lack of permissions on a registry key "HKEY_USERS\S-1-5-20".
By default, System, Network Service and Administrator accounts have "Full Control" and "Read" permissions on this registry key.
Because if the key has public access, it can be used by someone else at the same time.
Its a common problem which lots of Windows 7 users face.
Also when you checked System Properties, you got following error message: You must activate today.
In addition, product keys are only valid for certain versions of Windows.
Therefore, this method is not recommended, since you will simply waste time searching for a working key for your version of the system.