Gmod Crash when i start

Hey i was woundering if anyone could help me with my Gmod crashing

When i start it gets to about 15% loaded on the main menu and then Boom

it says something like

The memory (Numbers)at (numbers) could not be read please click ok to terminate program

not the whole thing but youl know what i mean ? anyone help ?

[editline]10:33AM[/editline]

No one ?

Specs please?