New message that my Windows 7 is not genuine

[Cassel]

Since a few weeks, I am getting a little popup saying that Windows cannot be activated. Even after rebooting the computer, that message has not gone away.

Since about a week, I am getting different messages about my Windows 7 not being genuine.

On the bottom part of the desktop it now says:

Windows 7
Build 7601
This copy of Windows is not genuine

Often, I get a popup in the corner asking me to activate my key. It says:
Activate Windows now
The activation period has expired.
Click this message to start activation.

Then at other times, I get a popup saying:

Optional update delivery is not working

You may be a victim of software counterfeiting.
To use all Microsoft windows features, such as all
updates from Windows Update, get the latest updates;
and receive product support, your copy of Microsoft
Windows must be validated as genuine

And i also "lost" my desktop as it is only black now.
I rebooted my computer today, thinking it would go away, but it didn't.

Any idea what is going on?