Launch problem !

Hi!

This morning I bought Garry’s Mod, download and everything, so after I run it, but nothing changes! I’m still on the computer screen what normal, desktop, web, steam etc, yet I went on steam and y’avait marked that I was in the game Garry’s Mod! Someone he solved the problem please! Or just knows a solution. Information for Windows 7 and I have Garry’s Mod the last version.
Thank you maybe advance.

[editline]15th December 2012[/editline]

Please help me ^^

Help me please !

Your specs would be nice to see.

Can you help me ?