Shut-Down problems with Tiger on mini

I just bought a new Mac mini on Friday and I am very new to the mac scene, but I'm having a problem. Every time I shut down the computer I get a screen that says I need to restart or hold down the power button for a few seconds. I ran Disk Utility and repaired disk permissions. Unfortunately I still get the screen on every shut down. If anyone can help with simple trouble-shooting directions it would be greatly appreciated.

Sleep is a better option than shutting down your computer for apple users most don't shut down , check your energy settings in system preference and see what the settings are.