teh poor n00b

For 0.23, I've had issues with the 2.5 meter heatshield not spawning in the game (as in it doesn't appear at all in the VAB, SPH, or in flight). Does anyone know why the 2.5 meter shield won't appear?

For whatever reason, on a fresh KSP file with no mods, some parts don't appear, and the parts that appear also don't work. I just downloaded the latest version and tried it and got the same result. Does anyone know why this is happening?