Very weird HW problems. Can someone diagnose
 

Ok heres the problem.

Intermittent reboots.

I know what everyone is going to say, powersupply, for sure, 100%.

Well just replaced the 1 yr old Aopen for a 400watt asus. and still, no go.

Temperature is not affecting this, because I will hear it reboot, in the middle of the night, while the computer is idle.

The CPU temps are around 35-45*C, and case about 30*C.

The rest of the computer is:

sempron 2600 (underclocked it to 1800+ and still same results)
MSI KT6V mb (reset to bios defaults, makes no diff)
512 kingmax mem (could this be the prob?? ive tried reseating it)
120gb seagate barracuda
160gb wd
liteon dvdrw
and think thats everyting hw wise.

Also, I have tried hooking up the computer downstairs, incase maybe there was something screwy going on with my power up here, but no nothing.

Thanks in advance for all who replys!

turn off automatic rebooting in XP and check the BSOD errors and the error log. Next, run Memtest for a couple of hours. You can also run Prime95.

There is no blue screen coming up.

It acts exactly as if I just pushed the reboot button.

I cant really run any testing programs because the sytem reboots wont stay up for more then 5-10min

When it next reboots, note the time.
Start> Run>
eventvwr.msc

Read through your system and application logs for about 5 minutes before the noted time.
You should see something there that will be a lot more informative.

Sisoft's Sandra is a good diagnostic tool that can give you a lot of good info re your pc and offer suggestions to help it perform better.

im now running at 1.1ghz and its been stable 45mins.

temp is still around 40*C, but i cant understand???

the cpu ran fine for at least 4months, why all of a sudden would it not wanna run at normal speeds (2.3ghz)

If the side of the core got chipped or otherwise damaged when you were installing the heat sink, that could cause this kind of problem. It's pretty easy to do with flip-chip designs. Not sure about the physics behind it all, but chipping the edge off of the silicon can have all kinds of strange effects on a system's stability, including random reboots, weird power surges (the CPU draws a lot of power, so if it decides to suddenly short out for a moment, power fluctuates like crazy in the system). My advice would be to verify your theory by purchasing a processor somewhere like Frys where you can return it if it wasn't the problem. Try it out in your system and see how it works. Best case: it works fine and your problem is solved. Worse case: problems persist, you take the new processor back, and try swapping the motherboard.

Has this always happened? If it hasn't then what changed?

Check your clock speed and multiplier. I have a kt3-Ultra2-BR from MSI and had my FSB set right, but an incorrect multiplier for over two years.
Can you say slow burn? By forcing the system to run at 334 fsb instead of 333mhz for years, it slowley burned the system up.
I started getting random reboots without an error message, exactly as you described. No memory dumbs or error logs. Took me three weeks to figure it out.
I decreased the clock multiplier and brought the clock cycle down to keep the cpu at 1ghz instead of it's native 1200ghz support. It's been stable for 4 months, but I lost 200mhz, and trying to bump the chip back to 1200mhz just causes the problem to start again.
Even worse, the fsb was wrecked through the inadvertant overclock, and now randomly bumps back to 334.5 according to Sandra.
Now I just bide my time to an upgrade.

Yes it had been occuring for about 2 months. The cpu (sempron 2600+) was purchased around sept and ran fine at 2800+ (183mhz * 12.5), default clock setting for a 2600+ is i think 160 or 166 * 12.

Anything higher then what im running now (100x11) causes the system to reboot within minutes.

I guess from what you guys have said my cpu is pretty much toast... Doesnt really make sense to me, as cooling has never been a problem, right from the start I had a nice thermaltake heatsink/fan combo, and 2 nice case fans keeping the cpu temps under 50*C at all times...

What would changing the Vcore make? would raising it help the stability of my system, or not? I am unsure of what it actually is. core voltage of what?

I had this one...

Voltage regulator on mobo..

Does your BIOS have a voltage monitor screen? Can you access your voltages on your desktop? If you see voltage swings outside the normal operating range it will cause a reboot.

-SF

Raising it would make it more stable at fast speeds, raise it too high and it'll burn the processor either slowly or quickly. Vcore is the voltage of the CPU.

In other words, you had the cpu overclocked when this all started. Problem identified then.

I would agree with this. If you had the CPU overclocked when the problem started, then that is probably the cause. I would double check the BIOS though, just in case.