just bought garry's mod today and it seem to prob loading the map

when i select play singleplayer, then select a map and start, then it take forever to load and freeze halfway

so i need to press ctrl+alt and del to close the game,when i did that,a box popup saying hl2.exe stop responding

my pc spec
core 2 quad Q6600
4GB DDR2 800
Ati HD 4870
WIN7 Ultimate X64