CPUs almost never die. 99% that it's the board.

Even when the CPU is dead, or without a CPU at all, the board should start. You should notice that other components (fans, hard drives, optical drives, if any) are getting power. Eventually the board would beep on you.

If you get none of that, then either the boards are both electrically dead (meaning some very fundamental component in the power circuitry is shot), or it's the PSU.

Just last week I had this problem with my Asus P4P800dlx.

It required about 3 times to reseat the cpu and has worked perfectly since. I suspect the cpu connectors in the socket get oxidised over
the years and need to have a few attempts to get the electrical juice flowing properly. Mine hadn't been turned on for about 6 years.

Please post photos just in case anyone picks up something that isn't right and could be causing the problem.

Make sure You have the 4 pin atx connector installed where required, definitely the P4 motherboard will have one.

Yeah, I plugged in the 4 pin ATX connector properly and all the other stuff.
About the Pentium 4 motherboard, what's weird is that the LED that indicates it has power turns on and stays on as long as I keep on the PSU, it just doesn't start on whatever pin to turn it on (damn oldschool motherboards that don't have built-in power buttons... I never understood WHY... I'm glad my current MSI Z97 Gaming 7 has one)

As soon as I go there, I'll take some photos of each motherboard and in great detail, I'll also take a photo of the processors (above and their pins below), hopefully with my reflex's macro feature.

That LED simply indicates that there is power on the +5V Standby rail. It tells nothing about the other rails of the PSU or anything else about the general state of the board.

Elia1995 wrote:

I tried to "jump start" them with the classic screwdriver trick, but nope, they're both dead...

Are you sure you're using the right "trick" ? Different motherboards may put the required pins in different positions. Also, your screwdriver could conceivably be electrically insulated.

Yeah, I tried every possible combination of pins and that screwdriver worked fine to jump start all other motherboards I've tried so far.

I'll try to rip a power button off an old chassis...

Did you try jumpering non-adjacent pins on the connector block? I have come across more than one motherboard in the past (Dell FTW) where the pins for the power switch were not next to each other.

That one I didn't try yet, actually, great idea !!!

Just to verify your power button pins : http://www.manualslib.com/manual/601858/Abit- … ?page=19#manual

Also, if the motherboard battery is low (not completely dead, just too low), it is possible that the RTC crystal has stopped ticking and won't start even if 5VSB is available from PSU. I've run into a motherboard that needs a ticking clock to operate so it won't poll the soft power button.

So, remove all the power from PSU mains switch and wait for the 5VSB to fade away. Remove the motherboard battery (measure it if necessary) and preferably put in a new one, or just give it 5VSB from PSU without battery. Then try the front panel power button, with screwdriver or real button.

Since I have another spare CMOS battery, I'll try swapping it in the Abit NF7 mobo.

Small update:
The Abit NF7 now turns on after I changed the CMOS battery.
On the first try I heard an unpleasant BANG, but it "works" or at least it turns and stays on.
But I don't get any video, I tried with a Matrox graphics card and now with an nVidia AGP card but with neither I get video… help

I'd do a fully recap on any ABIT motherboard before using. They are known for using bad caps on almost all models.

Also, try cleaning the whole board with a brush and isopropyl alcohol (99%+). Old batteries should be removed too.

I found one of those cylinder-shaped condensers kinda blown from inside, I'll try to change it if I can find a spare one at an hardware store.

Ok, time for the pictures (finally) !!!

I'll have to link them because they're HUGE, thanks to my Canon EOS 550D...

Here's my beloved (well, it was the motherboard of one of my early Windows XP computers) Abit NF7:

Here's the AMD Athlon in its Socket A:

I couldn't tell if that bit above the chip in the middle was dirt or some remainings of the ancient thermal paste it had before I took off the cooler to check what CPU it was.... either way this didn't come off with the alcohol and I took the picture before I cleaned it (notice how much dust was still there).

And here's the Asus Intel Pentium 4 motherboard:

As people below made me notice, it's an Asus P4P800.

Elia1995 wrote:

And here's the Asus Intel Pentium 4 motherboard: […]
Show full quote

And here's the Asus Intel Pentium 4 motherboard:

I dunno for sure which MODEL it is, but it's certainly an Asus, look how clearly it is written over there !!!

Looks like it's a P4P800 (it's mentioned between the PCI slots 😜).

Thanks for fixing the images 😀

They are not down; he just used a service that does not allow hot-linking.

Weird... I've always posted them like that with imgur... hang on, I'll reup them.

Tetrium wrote:

Looks like it's a P4P800 (it's mentioned between the PCI slots 😜).

Oh damn, I'm blind 🤣

Elia1995 wrote:

Weird... I've always posted them like that with imgur... hang on, I'll reup them.

Tetrium wrote:

Looks like it's a P4P800 (it's mentioned between the PCI slots 😜).

Oh damn, I'm blind 🤣

P4P800 Deluxe to be precise. Exactly the same as mine, except possibly a Rev 1, mines a Rev 2, says so on the motherboard.