Visual Studio is responding slowly


i’m facing a strange error:
The whole day VS was working fine. But then it started to react kind of strange…
If i open VS (without a Project) the center screen is blank. Then, if i make it windowed and fullscreen again, everything is looking fine. Then i click on a Recent Project - nothing happens. I have to change the window again to see the project. If i type something into the textfield - nothing happens. Resize Window → it shows me the change.
The Menubar is just working fine. I can go into every menu and they are all responding normal. Also the Toolbar is reacting normal. But everything below the Toolbar is not working (also the Solution Explorer). It seems like its not updating the graphics.
But if i open VS as Administrator - its working just fine! No issue at all.
There is no HDD/SSD activity, no high-CPU usage or extreme Memory usage if the error occurs.

I tried to reinstall VS, but didn’t do anything. Does anyone got an idea or solution?

Unreal Engine 4.5.1
Visual Studio 2013 Community
Fresh installed Win7 Ultimate (~1.5Week old)
Core i7-4790K
MSI GTX970 Gaming4 (Driver: 344.65)

Visual Studio is laughing at me! Now it is working just fine - but how long? And i didn’t do anything. While is was tipping this post, i reproduced the error. And now - 1min later - it is working.