No POST, Wits End

[archvras]

I've decided to post on this forum after two months of being without a PC (it's been hellish, to say the least).

My problem first arose when I woke one morning to find that my PC wouldn't POST. When I powered on, I would get a brief flash of the motherboard light and a momentary spin of the fans but nothing beyond that. I was very confused because I had not had any issues for the last two years, not even the night before. That day, I drove to the nearest Best Buy and picked up a CORSAIR 650m to replace my EVGA fully modular 650w 80+ Gold, but I had no luck there. The PC in question also had an i5 6500, an MSI R9 390, 8gb G.Skill Ripjaws V, a Western Digital 1tb, and a basic ATX Gigabyte mobo that cost around $100 in early 2016, all packed into an NZXT S340.

Flash foward to a month ago, I ordered a Ryzen 1700x and a Gigabyte AX370-Gaming, figuring it was a mobo and/or CPU problem. I built the machine and, what do you know, I had the exact same issue as before. After that serious let down, I sent in an RMA at Gigabyte for the mobo, shipped it, let them do their work, and got it back only for it still not to work. That was last Friday. I'm hesitant to do the same for the CPU as my original problem still remains persistent, and I don't really believe in coincidences. BTW I didn't replace any other parts in the PC besides the CPU/mobo. 

So that leaves me to now. I know it isn't a PSU issue, and I've tried booting it without the RAM, GPU, and SATA connected, all in different combinations, all to no avail. I hope there somebody reading who can assist me, so thanks in advance! 

[Airdragonz]

Are there any error code lights or code readouts or beeps coming on the motherboard? And if possible, can you be a bit more descriptive of the issue? How long does the machine stay on/fans spin after pressing the power button? Does it boot loop or just shut itself down?

[WereCatf]

You used the RAM from the i5 on the Ryzen? Should try another stick of RAM.

[Alex Atkin UK]

18 minutes ago, WereCatf said:

You used the RAM from the i5 on the Ryzen? Should try another stick of RAM.

Or at least try them individually to see if just one of them has died.

[archvras]

3 hours ago, Airdragonz said:

Are there any error code lights or code readouts or beeps coming on the motherboard? And if possible, can you be a bit more descriptive of the issue? How long does the machine stay on/fans spin after pressing the power button? Does it boot loop or just shut itself down?

No to answer your first question. The machine stays on only momentarily before turning back off, it does that only once

[JHDavis]

I doubt this is the problem, but do you have too many standoffs in? it could be shorting the board. But RAM sounds more like the issue, potentially. Like WereCatf and Alex said, try going through the RAM.

[0x1e]

13 minutes ago, JHDavis said:

I doubt this is the problem, but do you have too many standoffs in? it could be shorting the board. But RAM sounds more like the issue, potentially. Like WereCatf and Alex said, try going through the RAM.

I agree.
If it powers on once and then needs to be reset from the PSU then it sounds like a short.