Windows 7 Windows 7 reset itself :(

Today, when I booted up my computer, it said 'Please wait.. Configuring your desktop'.
And when it loaded up, everything on the computer was reset.

Fortunately, after looking everywhere, I found everything (My documents, pictures, music, videos, etc). But if I go to the start menu, and click on a program, instead of opening it, it starts installing it...

On the pics, as you can see, there were some programs on the desktop. But when I clicked on it, it started installing it. Also, as you can see, the Documents, Pictures, Music folder has been reset.

What could the reason be, and is there a way to prevent this in the future?

PS: I did some customization to the computer, such as installing themes, custom background, etc... Could that be the reason?

Thanks.