I just put together the following, and when I turn it on, the CPU cooler spins (and the LED light on the CPU cooler is on as well). But after a few seconds, the whole thing just powers down; both the CPU cooler and the power supply's fan stop. While it was on for a few seconds, I didn't hear any beeping sound nor saw anything on the screen.

* AMD Ryzen 2700X

* AB350 Gaming-ITX/ac: The little sticker on the BIOS chip says "P4.60", which is the latest version as of now ( https://www.asrock.com/mb/AMD/Fatal1ty%20AB350%20Gaming-ITXac/index.asp#BIOS" rel="nofollow - https://www.asrock.com/mb/AMD/Fatal1ty%20AB350%20Gaming-ITXac/index.asp#BIOS ). It should be compatible with Ryzen 2000 series.

* Corsair Vengeance LPX 16GB CMK16GX4M2B3000C15: This is on the Qualified Vendor List ( https://www.asrock.com/mb/AMD/Fatal1ty%20AB350%20Gaming-ITXac/index.asp#MemoryRR" rel="nofollow - https://www.asrock.com/mb/AMD/Fatal1ty%20AB350%20Gaming-ITXac/index.asp#MemoryRR ), so I guess it should be OK as well.

* ASUS Radeon HD5450: I have no need for anything more powerful than this, and besides, this is the only one I have. I tried it on an equally prehistoric motherboard and it worked fine. At least it's a PCIe card, and it fits perfectly to AB350.

* Zalman ZM600-HP: It's an old 600W power supply that had served well for a long time before I decommission a few years ago.

I'm out of clue, except that perhaps the power supply is underpowered or the graphics card is too old. I appreciate any suggestions or opinions. Thank you.

__

sol

well the specs for psu seem ok

may i suggest back to basics

install 1 stick of ram in slot a2

24pin power to board

8 pin cpu/eps power to top left corner of board

no hdd/ssd or dvd's

and also try if you can different options for the display output to monitor eg hdmi/display port/vga

try to boot be aware some systems can require a wait of incredible length 2-3 mins before bios screen

some reports of 3-4 cold boot attempts before signs of life also on first boot after bios flash of new build

other than that remove and refit cpu clear bios (battery out ) and retry

No beep is expected as the BM lacks a speaker, if you can scavenge one and connect it maybe it can give some clues about the problem via beep codes...

datonyb in his post above was extensive but forgot to mention also memory training, the PC should reboot three or more times in rapid succession to test the RAM frequency/speed installed on the system. The first time I experienced it scared me as I thought the PSU was malfunctioning and pulled the cord from it... ^__^;

AB350 Gaming-itx MBs have a speaker(buzzer) in package. Just have to plug in to respective  pinouts on  motherboard. if it's already plugged in, naturally expected beep sounds.

I just realized I'm out of thermal grease, so once I acquire some, I'll try the following.

* Start with 1 RAM stick.

* Disconnect HDD/SSD/DVD drives.

* Make sure all power cables are properly connected.

* Try all display connectors (DVI, HDMI, VGA) in the graphics card.

* Give it sufficient time, because initial booting might take several tries.

* Clear CMOS while I'm at it.

* Connect speaker. I didn't see a speaker in the box, though.

* Try different power switch. The problem I observed (i.e. the system powers down shortly after starting) looked similar to how it would behave if I keep the power switch pressed, so it might be worthwhile to verify.

I'll report back once I go through the list.

Not to nitpick but usually a PC speaker isn't packaged with a MB but embedded in the PC case.

Well, yeah I'm nitpicking. Also I'm not so fun at parties... ^__~

Speaker ) optional) comes in MB pack..................

spin up then power down sounds like psu fail to meet MB specs  for stability.

I tried again, and the following is the result.

* With everything suggested: I hear 5 beeps and then the motherboard shuts down. Pressing the power button doesn't turn it on again; I need to turn off/on the power supply.

* Without video card (Radeon HD5450): I hear 5 beeps and then another 5 beeps, but at least the motherboard doesn't shut down.

If I have to take a wild guess, I'd say it's the video card is to blame. Perhaps it's too old or simply not compatible. If that is so, I'd like a recommendation on something 1) affordable, 2) fits in Mini-ITX case, 3) quiet, and 4) preferably AMD instead of NVIDIA.

I have no need for anything other than the barest basic, because the choice was either 2700X or 2400G, but I needed more CPU cores than graphics.

There is one obscure option that is possible with the video card.  It could be a "pre" UEFI GOP (Graphics Output Protocol) version of the HD5450.  I updated mine years ago (BIOS flash to the VGA Card), so it works.  But if your card has an older BIOS, its possible that it might not actually work correctly as the MBs UEFI BIOS doesn't handshake with it correctly.

Here's a reference for it:  https://community.amd.com/thread/183390

The video card works when I tried it with a similarly old system, but it certainly was from the time when UEFI was even in the picture. VGA BIOS sounds like something worth trying.

I'm connecting the video cable from the monitor to the video card, not to the motherboard. 2400G works without a dedicated video card, but 2700X doesn't.

The 8-pin power was the first thing I checked. I think the system didn't even start without it.

As for the 5 beeps, it was about 0.5 second per beep. Not sure that's considered as long or short.

is csm switched on in bios ?

Hmm... if we are talking about Compatibility Support Module (CSM), then I'm not sure, because I can't even reach the BIOS/UEFI screen. I tried clearing the CMOS, though.

I just re-read what I wrote and realized that perhaps I should have worded differently to avoid misinterpretation. Anyhow, no, I haven't tried 2400G on my motherboard, so I don't know whether the motherboard is defective or not.

I'm seeing something inconsistent every time I start the machine. Without the video card, I usually hear 5 beeps and power down, but sometimes, the system stays up after the beeps. Some other times, it just powers down without beeps.

With the video card, I saw the BIOS screen 2 times, out of, perhaps 30 tries or so. At that point, everything looked normal, including voltage and temperature. I selected reboot (to boot from the USB device), but the system turned off during booting as it usually did.

Something else I noticed is that, right before the system shuts down, the CPU fan spins faster. Not sure that has anything to do with the problem, though.

So, I'm inclined to point my finger to the power supply now. After all, it was born many, many years before 2700X, so it might be insufficient to handle the demand. Would it be worthwhile to look into a replacement power supply?

Another protocol that you could do, is that old "strip everything down" move.  Take everything out except the CPU, and push the on button and see what it does.  Then, put in the video card, and see what it does.  Then put in one memory stick and see what it does.  A pain I know.  Wish there was more for us to go on!   I love a good mystery

It turned out to be the power supply; once I replaced it with a new one, everything worked just the way it's supposed to. The old power supply does have separate cables for the CPU, but it must be not sufficient enough to handle the recent CPUs. Perhaps that explains why the system passed POST a couple of times out of many, many tries.

I also noticed that if the little sticker on the BIOS chip says "P4.60", that *is* the BIOS version. http://i.viglink.com/%3ckey=d7d7aa5ced1ebc0821effbccab897fa0&insertId=362a794cffdca80f&type=H&exp=60%3ACI1C55A%3A20&libId=jkcvgv9y010009ks000DA3gn6yfm&loc=http%3A%2F%2Fforum.asrock.com%2Fforum_posts.asp%3FTID%3D9225%26PN%3D1%26title%3Dab350-gamingitx-ac-doesnt-post&v=1&iid=362a794cffdca80f&out=https%3A%2F%2Fwww.amazon.com%2Fdp%2FB00LP9GW3O&ref=http%3A%2F%2Fforum.asrock.com%2Fforum_posts.asp%3FTID%3D9225%26PN%3D2%26title%3Dab350-gamingitx-ac-doesnt-post&title=AB350%20Gaming-ITX%2Fac%20Doesnt%20POST%20-%20ASRock%20Forums%20-%20Page%201&txt=%3Cspan%3EP4%3C%2Fspan%3E%3Cspan%3E.%3C%2Fspan%3E%3Cspan%3E60%3C%2Fspan%3E%3Cspan%3E%2C%3C%2Fspan%3E" rel="nofollow - http://i.viglink.com/%3ckey=d7d7aa5ced1ebc0821effbccab897fa0&insertId=362a794cffdca80f&type=H&exp=60%3ACI1C55A%3A20&libId=jkcvgv9y010009ks000DA3gn6yfm&loc=http%3A%2F%2Fforum.asrock.com%2Fforum_posts.asp%3FTID%3D9225%26PN%3D1%26title%3Dab350-gamingitx-ac-doesnt-post&v=1&iid=362a794cffdca80f&out=https%3A%2F%2Fwww.amazon.com%2Fdp%2FB00LP9GW3O&ref=http%3A%2F%2Fforum.asrock.com%2Fforum_posts.asp%3FTID%3D9225%26PN%3D2%26title%3Dab350-gamingitx-ac-doesnt-post&title=AB350%20Gaming-ITX%2Fac%20Doesnt%20POST%20-%20ASRock%20Forums%20-%20Page%201&txt=%3Cspan%3EP4%3C%2Fspan%3E%3Cspan%3E.%3C%2Fspan%3E%3Cspan%3E60%3C%2Fspan%3E%3Cspan%3E%2C%3C%2Fspan%3E" rel="nofollow - I did mentioned it to the ASRock support, but they sent me a new BIOS nonetheless.

Thanks everyone for taking time to share your suggestions. Much appreciate it.