Garry's Mod not Starting

I just bought this game through Steam and I installed it at least four times, none of which got past the first loading screen. It would sit there and I would CTRL+ALT+DELETE to open the task manager and I would find Garry’s Mod “not responding”. Any help would be great.

For fun, do you own a Source-engine based game?

Could be the new update mess up. Though it could be above mentioned.