I bought Gmod yesterday, and every time I try to run it, the game gets to the loading screen and then I get a message that says hl2.exe has stopped working. 
Now, I haven't had this problem so much with TF2 or Zombie Master, which is why I thought that this was strange. 
I've also restarted Steam, and uninstalled and reinstalled the game twice. 
Hopefully someone can help me with this.

 Hi - this sometimes means that your computer isn't good enough to run it - or (more likely) you need to update your graphics card drivers.

There's a guide to updating your drivers here:

https://support.steampowered.

If the problem persists even after updating the graphics card drivers, a few people have reported success by adding -dxlevel 80 to the command line.

To do this, right click Garry's Mod in steam and go to Properties. In the window that pops up click the "Set Launch Options" button at the bottom. Now in that box, type "-dxlevel 80" exactly as shown (without the quotes).    

Thanks a bunch. 
I did the -dxlevel 80 option, and it works great now. 
Much appreciated, man.