"Could not load library client"

I am getting a message that says “Could not load library client”. I have a ticket open at steams help and support site and i have not gotten a reply yet. When I run garrys mod, it starts up and then i get a black screen. If I move the cursor over where the menu is I can hear it but I cannot see anything. PLEASE HELP!
O/S:XP
2 gigs of ram
core duo procceser

Right click Gmod in Steam, go to properties, then set launch options, type in “-dxlevel 81”, try that.