Gmod not working

I’m sure this has been asked countless times before, but every time I start garry’s mod it gets to the loading screen with the traffic cone guy then after a minute it says hl2.exe is not responding, I’ve uninstalled and reinstalled it many times, and it still doesn’t work, how can I get it to work?
My computers stats are: Windows Vista home Professional Intel Core 2 Duo CPU T8500 @ 2.4 GHz
4 Gigabyte RAM, and 64-bit OS.