Probably bad capacitors. They're used to filter incoming power. Replacement is usually required in this instance. There are some guys on here who have a lot of experience re-capping and can give you more advice.

There is 20 1000uf/6.3V rubycon YXG 8x12mm and 3 sanyo S.E.87 8x20mm with same capacity/voltage.
plus one small 100uf/16V stone 5x8mm

Do those sanyo branded have some other parameters or can I replace all 23 using same type?

If you know the exact voltage and Capacitance values for each capacitor you have to replace, then any brand name will do as long as you match those values. In fact, that's what some people here do - they use BETTER cap brands in their replacements in order to lengthen the service life of these old MBs.

The Sanyos and Rubycon YXG are probably ok. YXG lasts practically forever. It's not unusual for 15+ year old YXG to test fine.

The Stone capacitors OTOH are complete rubbish. Can you please post a pic of your board so we can see which caps you have?

Visually they seem fine.

If it doesn't even switch on the main power supply (are the fans not even twitching?) it's rather not a capacitor. What voltage is on the PowerON pin when you press the button? (it should drop near 0V)
Are any of the supply rails shorted to GND? You can look for scratched traces too.

marvias wrote:

Visually they seem fine.

Where are the Stone capacitors?

Your board does not need to be re-capped. h-a-l is correct. Your problem almost certainly lies elsewhere.

h-a-l-9000 wrote:

If it doesn't even switch on the main power supply (are the fans not even twitching?) it's rather not a capacitor. What voltage is on the PowerON pin when you press the button? (it should drop near 0V)
Are any of the supply rails shorted to GND? You can look for scratched traces too.

Fans do not rotate at all, nothing happens. When I press the button, voltage on power on doesnt flap or anything. Stays on 3V or 5V depending on PSU.
If by supply rails you mean pins in ATX connector then no, I do not see any shortage. Visually I do not see any trace being cut.

mockingbird wrote:

Where are the Stone capacitors?

There is only one 100uf on last image

If you UNPLUG the Motherboard power cable (20-pin), you should be able to test the power supply itself directly. If you SHORT (connect the two of them with a single wire) the green cable with any of the black cables, the PSU should turn on and all devices attached to it (CD-ROM/DVD, HDD, etc) should all power on as well when they receive power. You can then read all the voltages from all the pins on the 20-pin cable with a digital multi-meter. Please do not shock yourself doing this. At my old job, we had an actual PSU testing device that would tell you all of the voltage rails, test out Molex, SATA, even the 4/8 pin CPU and 6-8 pin PCI-E cables and let you know if anything was out-of-spec. Very nice. It also automatically powered the thing on by shorting that green wire to ground as soon as you plugged it in.

Once you've verified the PSU is fine, then let's look at the MB. Plug it back into the PSU, then what I would do is instead of relying on your switch, I'd find the two pins that are marked for the Power Switch and short them directly with a phillips or flat-head screwdriver - taking care not to touch any other pins. As soon as you short the two pins, the system is supposed to power on.

If that doesn't work, start poking around for culprits. I'd take the CPU out, then reseat it. It's a Slot-1, so it'll be tricky, but it needs to be fully seated. We don't even care about the fan yet. If the CPU is not in the socket, it's quite possible that the system won't power on at all anyway.

As part of my testing, I'd also take EVERYTHING off of the MB except the CPU, power cables, and some kind of speaker-header so you can get beep codes. See if you get anything. If so, then put 1 stick of RAM back in, power on again, note beep codes. If good, then put your graphics card back in and hook the monitor up and turn it back on. If you get power still, then at least you'll have a beep code AND a screen display. It should be reporting the 1 stick of RAM and NO drives (because we unplugged all the drives). Work your way one device at a time until something either fails (causes the system to not power on) or you're fully stocked and powering on (because all of the previous steps may have fixed the issue).

Since it's a power issue of some type, start with the FIRST AREA and follow the power from the wall all the way until you have a complete system. First, test the PSU (getting its power from the wall), then the MB and CPU combo (point of distribution), then the RAM, then the VGA card, then a HDD, then Sound, CD-ROM, network, etc. Work your way from the wall socket on out.

I was testing PSUs indirectly by plugging them to another computer so I assumed theyre fine. Also i tried three of them. I am using screwdriver to power it on using pins.

I am unable to get past step starting PSU via power sw pins on board.. It does not power on at all, no fans (not even fans on PSU) are spinning. Reseating CPU does not help, I tried it many times with multiple CPUs.
I guess starting psu manually by shorting that green wire while connected to motherboard is not a good idea 😀

Any cracks or discontinuities in the solder?

marvias wrote:

I was testing PSUs indirectly by plugging them to another computer so I assumed theyre fine. Also i tried three of them. I am using screwdriver to power it on using pins.

I am unable to get past step starting PSU via power sw pins on board.. It does not power on at all, no fans (not even fans on PSU) are spinning. Reseating CPU does not help, I tried it many times with multiple CPUs.
I guess starting psu manually by shorting that green wire while connected to motherboard is not a good idea 😀

Disconnecting the MB prevents any power surge from doing nasty things to such old processors that can't be easily replaced, if you know what I mean.

Nothing seems to work, I do not see any cracks in traces on PCB.
I thought about bringing it to someone who repairs electronics for living and has tools to debug, but cheaper will be to buy another motherboard.
Will also try to return this one, I bought it on ebay as working but seller did not bother much with packing (no bubblewrap of foam, just motherboard in LDPE bag put into paper box)

If it's an eBay buy, don't even mess around. Just apply for the refund and see if the seller wants it back.