Empty Buttons, Icons in Safari, Mail, Finder, ... since OSX Mountain Lion, a restart won't help. Can anyone help?

I'm really upset. I paid and installed Mountain Lion OSX and everything worked fine. After a while I noticed that in Mail and Safari and probably in some other Applications, some Icons/Buttons or something are missing. They work fine when I click them but they're not displaying for what they are. They suddenly just disappeared and I have no Idea why.

I uploaded you guys some Screenshots of my Problem. I hope someone can give me a suggestion for how to fix this problem because it's really annoying.

Cheers,

Robert

Screenshots:

Safari (missing Icons at the left side)

Mail (also missing Icons)

Mail (another Screenshot of Mail with missing Icons just like Safari)

Finder (This appeared when I tried to upload the pictures...)