Do you have a multimeter? Try measuring voltages on the power connector. Perhaps one of the voltage rails is going bad. Bad power could cause erratic/unstable behavior that keeps it from booting.

What exact CPU do you have? I'm a little foggy on Xeons, but I think there are some versions (cache size and voltage spec) that won't work in this board, or at least aren't officially supported.

Does the display thing tell you the BIOS version? It might need an update for the 550.. although if your system was called an "X550" it implies maybe that CPU was original to it.

I recently acquire the HP Kayak visualize x550 (which i believe that it is Kayak XW badgered)

Might be. I don't have it in front of me but it looks the same as the board in my XW, which I think had the model name "6/450".

For whatever it's worth, I think the built in screen thing has an option to show POST codes, but the one you're using is surely more usable and easier to see. The smiley face display on my system is so dim it's almost invisible even with a flashlight.

I'm impressed you got the board out. I tried to do that one time and gave up when I couldn't figure it out.
Even with the board out, I still don't see the internal battery. Do you know where it is? Mine died ages ago and I couldn't find it.
Luckily it was so long ago that I still had a PC repair shop in the neighborhood with random parts for sale - like a battery that plugs into those pins. I unplug it when I'm storing it, and it's lasted so far. But I'd love to know where the internal battery is, and whether it's something I should remove to prevent a leak.

Hi,

about the voltage, i did a quick check on 5v and 12v rails when the system is powered on and it show up ok, the values is within spec.
about the CPU, it is a SL3AJ 550/100/512 which i believe that it been there from the beginning.
about the bios version, i kind of forgot 😜

about the internal "battery", it in the following location:

i is not really a battery, but it is super capacitor. I did removed mine.
if you want to use battery pack, there are external battery header at the top of the board, near the scsi connector.

(you may need to add diode to prevent system from charging the battery)

to remove the mainboard, i had to remove all the screw that hold the cpu cage to the mainboard, remove the screw that hold the io plate to the case, remove the screw that hold the white plastic on the top, after that, go to the back of the machine, near the front, there are two circular plastic, push them inward and then push them toward the front. They are a little bit tight so you will need a ton of force. You can use flat head screwdriver to push them forward.

Thanks for the description of how to remove the board, and the info on the battery/capacitor.
Mine stopped retaining settings back like ~20 years ago, maybe 1yr after I had bought the machine on eBay. At the time I then went to a local shop and bought an external battery for it that plugs into those pins.
You know... I wonder if my "bad battery" discovery happened after I stored the computer for a while, when of course it would have drained since it's a cap. Maybe it's actually good. I should look into that next time I have it hooked up.

I've used the SL3AJ in mine and it worked, so that's probably not an issue. BIOS on mine is something.something.05 (the BIOS versions just change that last number, 05 was the last). I don't know what would happen with an older BIOS, but based on the name of your system that's probably the CPU it came with.

If you backprobe into the connector you might be able to also check 3.3V, and keep in mind there are some standby rails also in addition to the primary ones.
I guess another possibility could be the removable VRMs. It's probably difficult to probe those though. They used to be common and cheap on eBay but that might not be the case anymore.

If you probe one of those tantalum caps near the CPU slots, you might find CPU voltage there. If you're worried about shorting anything put tape around the probe. Negative can just go on the PSU case.
Trouble is, the slots have independent power supplies (separate VRMs) so you might have to probe a cap that's near the active CPU, and that looks like it would be difficult.
I don't remember what the spec voltage is for these CPU modules. If you can, also try to watch it while the system is trying to boot and see if it sags and looks unstable.

I don't know if this board will boot without anything on the battery circuit. Some motherboards have issues with that but I don't know for this one.

I'm looking at the dip switch settings in your picture, and I'm wondering what SW9 is. Could that be a bus divider setting for the PCI clock? Have you tried it both ways?