HL2.exe not working

Apparently this is pretty common since 13 rolled around but, I,m here to get answers. As it says in the description HL2.exe won’t work I’ve tried pretty much everything I could think of.
I’ve even tried completely uninstalling steam and re installing all of my source games. I’m using a 32-bit windows 7 home premium operating system and have a good processor and video card. If you know an answer instead of repeatedly opening gmod or doing the -dxlevel 81 thing then please tell me. It tends to end on post int systems on the facepuch loading screen.

Have you verified your game cache, and deleted your steamapps/garrysmod folder?