In most cases it is either like mentioned Dirt causing overheating or bad
power supply. As suggested clean out your computer. If it still reboots
after cleaning it out you likely have a bad power supply.

"Manny Weisbord" <mannyweisbord@crimest.invalid> wrote in message
news:3nct35pje23gut33rt3cbquls1oqm1nohc@4ax.com...[color=blue]
> [crossposted to microsoft.public.windowsxp.general]
>
> Kristoffer <guest@unknown-email.com> wrote:
>[color=green]
>>
>>Hello! I just wanted to ask why this is, a friend of mine has a
>>computer, its not vista doubt. It just Windows XP. So, it shuts down
>>without any error or anything, I mean like your surfing on the web and
>>the computer shutsdown and restarts, what can the issue with this be? I
>>mean, it just turns off, without any warning, It turns pitchblack and
>>the computer turns on agian. I helpt him defregmantating his computer
>>multiple times, but it still dosnt work.
>>Sorry for my bad english![/color]
>
> 1) More info is needed about the situation
>
> 2) Post your question to an XP group... this is for Vista.
> (I've taken care of that for you)[/color]