HL2.exe crashes in singleplayer, multiplayer works

Specs:
Processor: Intel® Core2 Quad CPU Q8200 @ 2.33GHz 2.34GHz
RAM: 8.00 GB
System: 64 bit
Video Card: NVIDIA GeForce 9800 GTX/9800 GTX+

Addons and such: None

Garry’s Mod was working fine until one day I fired it up to check out all the cool new toybox stuff and it crashed in singleplayer only. I clicked on a map (I tried multiple maps), waited for it to load, if I have my headphones on, I can hear the sound of weapons being spawned or whatever. I have gone into a few multiplayer servers and it works fine!

Steps taken to solve this problem:

  1. Reinstalled - Failed
  2. Defrag game files - Failed
  3. Verify game files - Failed

If anyone would be so kind as to lead me in the right direction, I would greatly appreciate it.

What addons do you have?

None, as I have re-installed the game.