Do you have a load on the PSUs? I think those XT PSUs require some kind of load to function. If not that then they may be turning off due to another fault on your MB, which is better than destroying the board.

^this.
Some older PSUs require segnifigent load. A motherboard and a few expansion cards alone won't allways do it.

Try connecting up the power to a mechanical hard drive, that should do it from past experience (if you have one) or stack floppy disk drives. Anything that sucks lots of power.

I'm gonna guess from the clicking though that something might be poking the board. Try booting it outside the case.

I'm no expert but it sounds like you might have a short on the board, hence why they won't start. Do you have access to another XT or AT motherboard to try them?

Check between the board's 12V/5V rails and ground if there's a short.

Sometimes tantalum capacitors on the voltage rails can go bad and when they do, they basically become dead shorts which will trip the PSU's short circuit protection.

You could also try to plug a crap ton of HDDs on the PSU and turn it on (without connecting the PSU to the motherboard), preferably older MFM HDDs will work wonder, but SCSI HDDs (especially 10K+ RPM ones) can work as well for the purpose of loading up the PSU.

Use the table I provided below (pulled from Wikipedia) for reference to know which pin does what. You can match the PSU's pins to the corresponding pin on the board.

SodaSuccubus wrote on 2020-10-01, 07:35:

^this.
Some older PSUs require segnifigent load. A motherboard and a few expansion cards alone won't allways do it.

Some early IBM PCs had a power resitor across the +12V to make the PSU start. Yes, older PSUs may need a load.

If you have a harddisk lying around, use that. It will draw enough to make it start.

Shagittarius wrote on 2020-10-01, 07:33:

Do you have a load on the PSUs? I think those XT PSUs require some kind of load to function. If not that then they may be turning off due to another fault on your MB, which is better than destroying the board.

It turns out both the floppies and the hard disk needed to be connected for the power supply to work. So one of the power supplies is actually good.

Here's a hilarious thing. Before I saw these messages about the load on the power supply. I decided to test a new power supply with an AT adapter on it. Well, double pop and sparks from the mobo. I was very pissed cause I was sure I fried the mobo. But the crazy thing is that is allowed me to identify and remove the busted caps from the mobo. Now I plugged in the old power supply and it's WORKING sort of...

So I inserted an oti-067 VGA card and it sometimes shows some glitchy CGA graphics when it's booting I can see the mem test is good. I tried a PS/2 keyboard with an adapter and it doesn't work.

Does anyone know how I can make the graphics card do VGA and make the keyboard working? I know this has nothing to do with the original issues. I can make a new thread if you like.

XTs and Turbo XT clones require a special keyboard as they use a different keyboard protocol rather than the one AT-class machines (which was also used on PS/2 keyboards). Unless you have a keyboard with a AT/XT switch underneath, or a true XT keyboard, you won't be able to use a PS/2 keyboard on this XT board.

oti-067 VGA card

do you have ANYTHING else to test with? I hate OAK VGA cards with a vengeance...

I'm using an OAK card in my 286 system and it works just fine.
Maybe the BIOS on that card in particular uses AT featuress or 80186 instructions?
If so, a "real" CPU like the NEC V20 could fix that (the latter).. 😉

Is the VGA card a true 8 bit card ? I have one old VGA 8 bit that gives odd noisy video but my Oak OTI037c works great on XT's. Also have some Oak 67 and 87 based ISA VGA that work perfect in 286/386 boards.
Added: have a few 16bit ISA VGA that have a jumper for 8bit mode and they work fine on XT's...(if you do not mind the back part of the card hanging out ;p )