When I hit tab one of my elements vanishes. Is there a setting to fix this? I’m using 2.53 and the file is far to big to attach
I also can no longer pan in my window.
EDIT:
Great, now not only when I hit tab the object vanishes but I’m getting a diamond shaped target in the UV window. The target is stuck in the lower left hand corner. But at least through a series of expanding and doubling and collapsing windows I can pan again. It only took about an hour of being jerked around to fix it.
I think you hit H in edit mode, which Hides selected vertices. Use Alt-H to unhide. It is a bit confusing that the object is still visible when you leave edit mode, but it will start to make sense.
I don’t know what your diamond-shaped target could be, other than uv-mapped, non-hidden vertices.
It’s not hidden. I’m not sure what I touched but it was on the left side of the keyboard when things went wonky
I’ve done and pretty much trashed my .blend file. I attempted to do some UV mapping, baking, etc. and wound up with a file that no longer renders anything I’ve touched lately, the right walls still vanishes when I hit Tab and when I start the game engine the flickering is so bad a blind man across the street had a seizure.
http://www.megaupload.com/?d=7665KNEE
I’ve uploaded the file onto megaupload in the hopes that somebody can tell me what I did wrong (other than everything starting with not insisting on hiring a true professional to do the work)
Like I told you, the right wall is hidden. Select it in Object mode, tab into Edit mode, and do Alt-H. Its mesh will reappear.
I’m still trying to figure out what else is going on in your file.
Edit: The flickering is due to doubled vertices in the right wall. Select it, go into Edit mode, W->remove doubles. At the top of the viewport will be reported how many vertices were removed. You may have overlapping vertices in other objects too but I didn’t look.
For repeating things like the tubes on the cart, you should try an array modifier instead of having hundreds of tubes.
Thanks for taking a look at the file. For practice I’m redoing the walls, floor, ceiling and lights.
By all means get a laugh out of the textures. The boss wants to see a model done wrong before they’ll authorize doing it right.
The textures aren’t packed in the .blend, so I can’t laugh at them! 
I’m still stumped why much of the model won’t render. So far I’ve tried recalc normals (which was needed), removing all materials, and appending all objects into a fresh .blend.
Let’s put it this way, the textured metal was supposed to be shiny metallic and came out looking like pond scum. Instead of a 1024x1024 image I had to make due with a 130x130 with bad lighting.
The rest doesn’t surprise me, I managed to screw things up as well as any noob under pressure. The revised model that I did last night came out looking a lot better (except for the textures). Lesson learned, DON’T WORK ON YOUR MODEL ANY MORE THAN PRUDENT/NECESSARY.
130 x 130? Why? That isn’t useful for anything but small objects, or Mafia Wars.
Other lesson: this modeling stuff takes a lot of practice.