PC turns off by itself, before it wouldn't shut down

[cosrocket]

My friends PC was not turning off, when choosing ?shutdown? in Windows XP it would just restart. It was also slow in booting up so I reformatted the hard drive which made things go much faster, when I left everything seemed normal and fine. He just called me and told me now the PC shuts itself off every so often, it happened 3 times today. It doesn't happen when he's using it, he leaves it on and when he comes back a while later it's turned off. So this is sort of the opposite of what was happening before. He does have an external hard drive connected which he says was turned off; I bring that up because I?m grasping at straws as to why this would be happening.
Does this have to be caused by a hardware problem or is it possible that it's a software problem?

 

[Slugbait]

Sounds like either power settings or S3...the system isn't "off", but is rather "asleep". This is a pretty good tutorial on S3.

 

[Athena]

It sounds like the machine is going into standby mode -- which is a good thing actually. Tell your friend to see if pressing a key on the keyboard wakes it up.

When/if a machine goes into standby mode is controlled in the power management options of the control panel. How deep the sleep is depends on the BIOS options (S1 vs S2) and whether or not USB devices are allowed to wake it up.

 

[OBLAMA2009]

i have a similar problem. i loaded windows xp onto a dell optiplex with sp3 and when i turn it off through windows it goes through the shut off procedure but instead of powering down it reboots. can you guys help me as well?