Need assiance with playing Garrys mod on Windows vista

Ok so Recently i just got garrys mod and i after its done i wanted to go play it so i open it
ANd it normally says Preparing To play garrys mod or something like that but after that disappears i go to a black screen my friend told me thats normal but it stays at the screen for about 1 minute then it minimizes and a box says Trying to respond and a green bar comes across and another minute later it says unable to respond and such like that
Does anyone know how to fix
Oh yes i forgot to say i have a Laptop so
Operating system : Windows Vista 64 bit
Ram:4gb
processor:Intel®Core™2 Duo CPU 2gb
Pleasehelp

What source games do you have installed?