gmod voicechat problems

Hello guys,

Gmod ain't no fun when you can't speak to you fellow players. Now i have a problem with my voicechat.
If i go into the Gmod settings in-game and i go to 'voice' it sais that voicechat is enabled, but the voice transmit volume is on 0.
When i put it higher, press apply and close the settings window and go on a server again, it still doesn't work. When i go to my settings agains the voice transmit volume is automatically set to 0 again. Can anybody please help me?

Kind regards, gameplayke