Walls and Floors Not Showing up?

[PrimusPalus 0]

I'm having a problem in the tutorial where I have to mine to proceed. I can't see ANY floors, walls, or ceilings... though I can highlight them. I have my pickaxe equipped but can't right click on the wall to use it. Is there a ways to fix this? Here is a screenshot of the problem:

 

 

You can see the texture problem... the guy in front of me is mining fine. I however have the pick equipped and can't do what he's doing.