Pc Rebooting Repeatedly - Read for Details

Alright, first off let me apologise in advance if I am not in the right section. Frankly, I don't really know what the issue could be! Let's start from the beginnng.

My boyfried has a PC that his dad custom built for him. And recently, it hasn't been acting right. Just last week we took the pc to his dad's house, because it wasn't wanting to run. We found out it was as simple as the interior needing to be cleaned out, brought it back, everything was fine.

And yet, just an hour ago I was playing Sims 2 Apartment Life on it, and all the sudden - BAM! It shuts off and starts rebooting. So I'm sitting here thinking that I may have accidentally manifested some sort of glitch in the game that caused the pc to reboot, and yet, it doesn't even get near the windows xp loading screen, and reboots again... and again... and again... it gets to the same area, and just reboots!

I haven't tried much, but here's what details I can give:
1. I tried taking the CD out. Still goes bonkers.
2. I tried forcing it to shut down by holding the power button. Nadda.
3. Since THAT, it now comes up with the safe mode selection screen. (safe mode/safemode with networking/yadda yadda) I've tried to load it with literally EVERY option it gives me. Denied.
4. Because it's a custom built pc (rather old, I'd say. 2002, maybe?), we don't have a cd for the windows XP. So I can't try that option.

I'd really, REALLY love to attempt to salvage the PC without having to resort to erasing all my games and such. If anyone can help me with this, I will be forever in yourgratitude.

Sincerly,
Zannah0I

 

The first thing to do would be to check the power supply output or swap it out with a power supply you know is good.

 

Well, the funny thing is, just about five minutes ago I went upstairs to check it again and it loaded up fine aftr it had been off for about an hour, give or takea few minutes. Yet, here's what happened:

1. The antivirus that's installed on it turned off. No an actual problem, seeing as the computer has no internet. We use it only as a gaming pc. Just thought I'd put this down incase it has something to do with it.
2. It asked to install something. "Unknown". Wether or not it was hardware, I don't know.
3. I turned it back off and called my boyfriend to give him an update. He asked me to tell him the temp of the PC. So I turned it back on. It was, like, 29C / 80F. (The one below the CPU temp) Not only that, but the pc started to do it again - restarting before it reaches the Windows XP loading screen.
4. One of the fans inside is making a funny noise. This is kind of heartbreaking, seeing as we just got it cleaned lst week.

This makes me think it MIGHT be a fan problem, but I'm not PC-Savvy and don't know for sure. I'm going to have the fans replaced eiher way, but could that be the issue? Or just a issue on top of another issue? When I turned the PC on and it worked fine, I only had it on for about three - five minutes tops.

I would also like to know how changing the power surce (I'm guessing you mean by plugging it into another outlet) could make it run better? I've been playing Sims 2 on it, in that outlet, for the last week and it's been running fine up until today.

 

Open the PC up, get an empty paper towel tube and find out which fan it is, probably the CPU or chipset would be my guess. Make sure the wires from the CPU fan are properly plugged in.

What the poster meant was the power supply unit(PSU) itself inside the box. I'd check the fans first since that's easiest. Might even be the PSU fan itself since it was that dirty. Don't open the PSU box unless you know what you're doing.