MacBook shuts down after 30 minutes

[HokkaidoTramp]

I have a 2009 MacBook, aluminum case, with 160 GB HDD. The computer shuts down after 30 minutes while watching movies or listening to music in iTunes. This happens when using battery or power adapter. Yes, I have changed the energy saver power settings to "never" in both battery and power adapter. I've also tried "3 hours", "one hour", whatever. No effect. 30 minutes is all I get unless I poke the return button before the 30 minute time limit. I took it into the Mac store and they ran a diagnostic. Found nothing wrong. Really annoying problem. Any suggestions? (Black Swan required three pokes to get through the movie. Forgot once and had to restart everything. My girlfriend is not impressed.)

 

[simsaladimbamba]

Tried this yet?
Intel-based Macs: Resetting the System Management Controller (SMC)

 

[HokkaidoTramp]

Smc

Thanks for the suggestion. I just gave it a try but to no avail - after 30 minutes it logged me out and put the computer to sleep.

 

[GGJstudios]

Try Caffeine.