Hey everyone.
I recently installed the 64-bit version of win7 (home premium). Before I had a 32-bit system running. Blender was working fine on that system but since the “upgrade” it’s not working properly.
Whenever I try to use the rendered shader (live render) in blender (cycles as the selected render engine, blender render still works) blender crashes. (Just the default pop up window: Blender has stopped working) (doesn’t matter if I choose CPU or GPU rendering) (Also blender does not crash when Ipress the render key… Meaning I can render single frames, but I don’t get live feedback)
Previously blender crashed after just opening the program without anything happening. I downloaded python seperatly and replaced the python folder in the blender version folder. After that blender started and the new error came up.
I reinstalled blender several times. (2.72 | 2.73 both installer versions and 64-bit) (and I also tried the zip version of 2.73) all did not work.
I think there might be a problem with the GPU drivers. (on the 32-bit windows I just downloaded them, here I installed them using the CD from the box. I allready tried to fix it, installing the drivers from the nvidia homepage.)
My PC:
GPU: Nvidia GTX 780
CPU: AMD FX™-8320 Eight-Core
RAM: 8GB
Mainboard: MSI 970A - G46
Allready a big thank you to all of you 
Update: I tried a 32-bit version of blender and it works… It seem’s like sth is corrupting my 64-bit programs (AC Unity is not working as well it stops at the small loading image)