Involuntary shut down

My macmini will automatically shut down after it has not been used for about 15 minutes or so. I have checked the power settings, etc. and can find nothing. It is a dual processor unit that is only about one year old. Any ideas?

Thanks in advance.

If you leave iTunes open and running will it shut off after 15 mins? Or are to talking you completely walk away from the unit and it shuts off?
Bryan

If iTunes is running, the machine stays on. If however, I simply leave a webpage or document open, the machine will shut down after 15 minutes.

is it the whole computer, or just the monitor?

check under screensaver settings (i think, i'm not on my mac now), and see if you have the screen set to turn off after 15 min.

I have the computer set to never sleep and to never shut down the hard drives, just to see if that would make a difference. It still automatically suts down. Any thoughts?

Thanks

Similar problem with my macbook. check firmware: http://docs.info.apple.com/article.html?artnum=303880