Sudden overheating for no apparent reason

[NiQ123]

Hi,
I have an old Pentium-4 (IBM ThinkCentre 8171) that I use as a mini-server, which started experiencing overheating problems for no reason at all. There were no hardware changes whatsoever when this started happening and no new software installation either.
I sure that it's an overheating issue because it doesn't seem to happen if I run it with the lid open and a big home fan blowing right on the CPU.
[Before I reached that conclusion I've already ruled out software issues (happens when booted from a PE as well), hard drive problem (same reason + chkdsk finds no problems), RAM problem (memtest shows no errors + problem still happens after changing memory sticks)].

Anyway, the fans seem to be working perfectly and I've already dusted the fans and heat-sink and replaced the thermal grease, yet the problem is still there.
I'm looking for any creative ideas before I declare the machine broken and throw it away.

Thanks.

 

[Lutfij]

1| What sort of temps were you seeing prior and what sort of temps are you seeing now to be alarmed? Is it just a warning during boot up?
2| Are the fans running at full blast?
3| Mind sharing the OS off which your system is running?
4| When running memtest86, did you run the test for at least 10 passes?

 

[NiQ123]

1| What sort of temps were you seeing prior and what sort of temps are you seeing now to be alarmed? Is it just a warning during boot up?
2| Are the fans running at full blast?
3| Mind sharing the OS off which your system is running?
4| When running memtest86, did you run the test for at least 10 passes?

1. There's no warning whatsoever, the OS loads perfectly but at some point the entire machine hangs. When this happens Speedfan usually reports a CPU temp of around 50 degrees. Unfortunately I've never checked for this before the issue began so I don't know what's the "normal temp".
2. Again, there's no way for me to know. This computer was built especially to be quiet. Even when the fans are running at full blast you wont hear it. They cannot be controlled by software such as Speedfan. I only know that they never turn off.
3. It's running Windows Server 2003 (I don't think that hardware could run any newer version).
4. No (I probably should have) but the fact that the problems continues even after replacing the RAM modules, combined with the fact that the problem stops when I place a fan on top of the open case (this keeps the CPU at a temp of around 38 degrees) makes me pretty certain that it's an overheating issue.