Preventing Macbook from going to sleep when connected to A/V receiver?

[rainev]

Hey,

I'm using a Macbook Pro in the clamshell mode, i.e. lid closed, connected to an A/V receiver via Mini DisplayPort, and whenever I turn of the receiver, the Macbook goes to sleep.

Is there a way to keep the computer active while having the "display" i.e. receiver turned off? I've tried using apps like Caffeine or InsomniaX without help.

Thanks.