Mac Pro restarts 5 mins after booting up

[ampnerd]

I'm having a problem with my Mac Pro 8 core (2009 model) where I will boot it up in the morning and five (approx) minutes later it will suddenly reboot. It doesn't make a difference whether I'm doing something on it at the time or if it is sitting idle.

Sometimes it will start to reboot and it will get as far as the Apple logo screen and reboot again, sometimes 2 or 3 times.

Once the machine has been on for a while it doesn't do this anymore, only when it's first powered up for the day.

Can anyone suggest what this might mean? A logic board going bad perhaps?

Thanks

Sean

[Satcomer]

Take a look at your logs (do NOT post the whole log on the thread) with the application /YourHardDrive/Applications/Utilities/Console. See the time your Mac decides to reboot. The log might show you a reason for the restart and you can then see if it is hardware or software.

Good Luck.

[DeltaMac]

Try an SMC reset - shut off, and unplug the power cord for 15 seconds. Plug the power cord back in, and boot up.
Does your Mac Pro also restart when you boot to another system? Booting to the installer DVD would be a good test for this. Of course, you would try this after the system has been off for a few hours - so rather than starting up in the morning to your usually software in the morning, boot to the installer DVD. Simply let it sit on the installer screen, or test the hard drive with Disk Utility (which wouldn't hurt anyway!) Let it run for 15 minutes or so, just to see if the system suddenly shuts down, or other power interruption. If that seems to work OK - do you have another hard drive, with OS X installed that you can use as a boot drive, or space on a partition where you could install your OS X system? A fresh system for booting would also help to know if it's a hardware problem, or some kind of system software corruption that causes the restart.
Be sure to also check the power cord for a secure connection.