I would try with yet another PSU of adequate power.

Then would try removing stuff, keep only barebone. Remove HD maybe to avoid damaging data.

End up with only mobo + cpu + psu + ram outside the case and see if it stays on.

No miracle, troubleshooting takes time.

I have already tried that.

The PSU is new. 500 W

Unplugged CD-ROM, HD and floppy. Didn't work. Same behaviour.

Must I take out the videocard too, even if there is no video signal to see what's going on?

EDIT: One other thing I forgot to mention: the old PSU had an odd power plug that was connected to the front of the case to light up some fancy leds (showing temps and such). The new PSU DOESN'T HAVE this plug but I think it SHOULD NOT MATTER.

Make sure it's not shorting out on anything.
Also verify heatsink is on correctly (although you said it shuts down a couple of seconds after boot so it's probably not that)
Also try clearing the CMOS

I will check the heatsink too just in case. I could also try unplugging/cleaning/replugging the two DDR modules.

I would clear the bios with a jumper first to reset it to factory specs.

Second, I would check if the fan on the cpu is connected with a 3-pin cable to the MB. If it is and the fan is old, it's possible that the motherboard is shutting the computer down because it has a protection where if it doesn't see the cpu fan spinning at the correct RPM's, it will shut it down to protect the cpu. I've had this happen to me and replacing it with a new heatsink/fan fixed the problem.

Yeah I think the fan it's connected this way. If I remove the bios battery, will it reset too?

Yeah removing the battery is easiest just make sure the PSU is unplugged for 30s to 1 minute.

Thanks. I will try it tomorrow so it's going to be unplugged all night long. Ehrm I think you mean cutting off power for 1 minute before replugging the battery. 😁

Also im not sure about this, but removing the battery might not reset the bios properly and only reset the real time clock. Newer motherboards keep the bios in a EEPROM and the battery is used for RTC. Dont know about your particular board, jumper may be more reliable

And just how this works? putting a jumper on the pins?

eL_PuSHeR wrote:

And just how this works? putting a jumper on the pins?

Correct or something metalic like a screwdriver blade or knife blade, many times it's across pins 2 ~ 3 to clear the cmos.

You should also try removing *all* the RAM modules and note if the BIOS gives you a steady long beep code, usually indicating it can't initialize the memory or no memory found.

This will tell you that one or both the memory modules are faulty or perhaps the memory controller on the mobo is faulty.

Right, best is to consult mobo manual to confirm exactly which pins you need to short to reset the bios to default.

You could definitely remove ram and video card, keep only cpu on the mobo. It will not post, but it should at least stay on and beep at you. I would also take the motherboard out of the case as a final test. Install it on clean cardboard and try to power it, to rule out the possibility of the case shorting something.

If computer still shuts itself down in those minimal conditions,
then its very likely the mobo. Since the issue started with a dying PSU, could be that the dying psu sent a funny voltage before death and damaged something on the board.

Good luck!

Yes, good thoughts about the dying PS Unit taking out other components, I've seen this happen and it has happened to me personally on occasion too.

Not fun to troubleshoot but it is something that needs to be done.

That motherboard is an older Socket 478 based on the SiS chipset if I'm not mistaken.

Maybe time to look at upgrading if your friend can afford it that is.

Thank you very much for the replies. I have downloaded the PDF manual where it shows the process of resetting bios using a jumper. I will try today all suggestions you have made.

I have a further inquiry: If I take the board out of the case and plug just the psu (without those tiny power, hd leds, wires), how do I power it up?

BigBodZod: The chipset is Intel i848P MCH (ICH5) I think.

You can just short temporarily/quickly across the pins you would connect the "power on" wires to. Touch them with a screwdriver for example. The manual should say which pins this is.

Thanks. I will check manual on what pins are.

This is what I tried so far:

+ Clear CMOS by using the pins stated on the manual.
+ Remove RAM and cleaned its contacts.
+ Remove everything else attached to mainboard.
+ Power it up -> Result -> same behaviour. It powered down after 10 seconds or so.

Now I have taken the board out of the case. I am going to try shortcutting the wires for power. I will post back.

The screwdriver trick worked. Heh, that was fun.

But the behaviour is just the same. The board powers up and shuts down after 5-10 seconds. I have tried everything everyone so kindly suggested so I am assuming the PSU destroyed something on the mainboard when it dies, so now I must try to get a replacement mainboard.

EDIT: Forgot to add that I have tried also two different new PSUs (500 and 600 Watt).

I had a similiar problem testing a s775 PC, started up but died a few seconds later - turned out to be the cpu overheating(and probably the bios safeguard acting up), I hadn't installed the cooler tightly enough/too little contact....

I can do a few tests more (check the heatsink), but we are already looking for a new setup. I am being asked for 70 € for a socket 478 board. I think it's not worth it. A new system costs about 250-300 €.