Hard to say. MB's can cease working for all manner of reasons.

Proper diagnose would involve detailed visual inspection and electrical continuity testing, among other things.

*Can* be the caps.
I had a new FIC PA-503+ last week that had been stocked for more than 20 years, never been used, dead.
I measured the CPU core voltage and is was about 1.8V no matter what the jumpers said. Nominal voltages should have been between 2.0V and 2.9V
None(!) of the caps was bulged or leaky!

After a complete recap it worked perfectly.
A picture of your Asus P2L92 would be a good idea, so we can see what´s on it.

After such a long storage time electrolytics can be deformated. This in theory is reversible by having them connected to a DC voltage for a longer period of time. In many cases the result is unsatisfying. That´s why I prefer replacement by low esr 105° caps by renowned brands like Rubycon, Panasonic, Nichicon or Nippon Chemicon.
You always should go for brandnew capacitors out of current production - no "New Old Stock" - for the very same reason.

majestyk wrote on 2022-09-17, 17:51:

A picture of your Asus P2L92 would be a good idea, so we can see what´s on it.

Are you referring to the cap brands?

Private_Ops wrote on 2022-09-17, 17:54:

majestyk wrote on 2022-09-17, 17:51:

A picture of your Asus P2L92 would be a good idea, so we can see what´s on it.

Are you referring to the cap brands?

Yep!

majestyk wrote on 2022-09-17, 17:56:

Private_Ops wrote on 2022-09-17, 17:54:

majestyk wrote on 2022-09-17, 17:51:

A picture of your Asus P2L92 would be a good idea, so we can see what´s on it.

Are you referring to the cap brands?

Yep!

Not a complete set.

1 x Sanyo 360uf 6.3v (Purple)
2 x Sanyo 510uf 6.3v (Purple)
1 x Rubicon 1000uf 6.3v (Tall)
10 x Rubicon 1000uf 6.3v

The ones in the voltage regulator section (CPU) plus the ones beside the RAM slots are Rubycons and some Polymers - perfect! I wouldn´t think of replacing them at the moment.
Asus used high qualty electrolytics in many cases, but sometimes (maybe due to availability) they used inferior components, so you always have to check this first.

You should first inspect everything carefully for any damages (also the traces at the backside). The contacts inside the CPU-slots like to make troubles, too.

majestyk wrote on 2022-09-17, 18:09:

The ones in the voltage regulator section (CPU) plus the ones beside the RAM slots are Rubycons and some Polymers - perfect! I wouldn´t think of replacing them at the moment.

Visually, yes, unfortunately I don't really have a proper way to test them right now (excuse for more tools!).

The rule of thumb here is: If these Rubycons look good, they are as good as new.
I can´t identify the Polymers (the violet ones), though. (There are some cheap brands that tend to age.)

Speaking of new equipment - you could buy a POST-card and a decent multimeter for measuring the voltages.

majestyk wrote on 2022-09-17, 18:16:

The rule of thumb here is: If these Rubycons look good, they are as good as new.
I can´t identify the Polymers (the violet ones), though. (There are some cheap brands that tend to age.)

Speaking of new equipment - you could buy a POST-card and a decent multimeter for measuring the voltages.

I have an ok meter (an Extech unit, got it when a ground on one of my vehicles went and shut down half the coils). A POST card, yea, I should get one.

Thinking on it, I want to recap this board, if for nothing more than something to do. Caps aren't terribly expensive.

What would you guys recommend the electrolytics be replaced with? Mouser has some panasonics (FR I think it was) that look to be a good match but, reading various forums the ESR needs to be close (or better?) so that throws me off a bit.

Rubycon YXG series is still in production, but they're probably only the "tall" version. You can measure their diameter and height to verify. Digikey lists a shorter version, but they're out of stock with a minimum quantity of 2000. I've also heard of those purple Sanyo OS-CON caps failing.

It doesn't really sound like bad caps when one of the symptoms is 5V going to the fans.

I don't think those purple caps are polymers .

1 P2L97
2 why not do some basic measurements first? install only cpu, connect psu, stick one multimeter probe into molex black wire socket, flip the board on its back, start it up and measure:
-DC voltage on capacitor pins next to CPU socket, capacitor pins on both sides of DIMM socked
-AC voltage on capacitor pins next to CPU socket, capacitor pins on both sides of DIMM socked
flip it back
-DC voltage on Q13 next to ASUS chip and P2L97 print

there should be around 2V next to cpu, 3.3V next to dimm, should be no AC voltage. Make super double sure to not short anything.

Yeah...No such thing as Asus P2L92 afaik... maybe P2L something like P2L97 or P2L98 (hp oem) but not a P2L92 unless it is some odd-ball oem not listed at Asus, theretroweb.com or even Google ;p

verysaving wrote on 2022-09-18, 00:17:

I don't think those purple caps are polymers .

Yes they are. It´s quite an early model, Sanyo Oscon:
https://sg.rs-online.com/web/p/aluminium-capacitors/1882926

Note there´s no vent on the top.

Horun wrote on 2022-09-18, 05:09:

Yeah...No such thing as Asus P2L92 afaik... maybe P2L something like P2L97 or P2L98 (hp oem) but not a P2L92 unless it is some odd-ball oem not listed at Asus, theretroweb.com or even Google ;p

Typo on my part. Yes, its a P2L97.