There are two consols in the game. the chat consol that comes up when you press enter and a command cosol you open using the F5 key. Putting /devcommands in teh chat consol doesn't do anything.

You have to have -console added in the start up string Steam passes to the game. Its under the "manage", properties, general, menu for the game. Then look for "launch commands" and add -consol and restart the game.