no game sound in Black Ops 2, but can hear live chat...

[DesiPower]

Bought using steam over the weekend, I can hear people talk but no game playing sound like shooting, exploding dying and all that... any idea anyone? maybe some files are corrupt? I checked all the settings and everything looked OK. As its freshly installed I did not play around with any other settings...

I am using onboard Realtek ALC892 sound on this mobo