Level Editor Problem

[Mine Turtle]

Hi, it's me again with the same problem. If I press space, or if I click on the "Enlarge Current Viewport" button, this will happen (as Attachment). I can't move the screen with alt+mouse and I can't place anything. I think, it doesn't work because my render mode is on "Shaded", but if I put it on "Wireframe" then it works, but I can't work with wireframe it's just confusing and awful. I tried everything! I tried to map sth, and then press space, but it didn't work either. Please help me

try reinstalling the tools. if that doesnt work, then im not really sure :S