Mac Mini Power Failure

Hi
I have a Mac Mini (purchased 2005)
recently it has started to turn itself off after only being on for 5 minutes or so.
I have changed the settings to enable it to restart when there is a power failure but when it turns off it doesn't restart. I have to unplug the power cable from the mains and the computer itself for a minute or so and then when i plug it back in it will restart automatically due to the settings changes however it will then cut out after a few minutes again.

Can anyone help. i dont know if it is a problem with the power cable or something with the computer itself? Is it possibly it could be something to do with a heat problem, it doesn't seem as if it is getting too hot but i have had this suggested to me?

I have tried resetting the PMU and the same problem still occurs.

Me too, but a bit different. My Mini starts fast, runs for 20 minutes, then shuts down bam! I suspect heat. Maybe a loose chip? Did you ever resolve this problem?

Thanks,

Stbdtack