Q: Button icons have disappeared

same here. Macbook Pro Mid 2011, Mountain Lion, upgraded from Lion.

try a safe boot (start up the computer with the shift key held down)

Safe boot does not work!

use disk utility to verify your startup volume

is the same problem happening in another user account?

I am having the same problem on my rMBP. It happened a month ago. I then completely reinstalled the OS and didn't use migration assistant. The problem went away.

Now, a month later, my MBP woke up from sleep and wouldn't allow me to open Safari. I rebooted, and now my icons are gone again!

I did install the latest MBP update that was released (or at least noticed by me) today. I recall doing the same thing back a month or so ago right before it happened the first time.

This also seems to be related to:

https://discussions.apple.com/thread/4589599

I found another thread that relates as well:

https://discussions.apple.com/thread/4172568