Hmm. Opened another working PC and trailed power connectors from that PSU to the mobo on the failing PC. Still no POST. Not conclusive as the mobo on the failing PC wants an 8 pin ATX plug (2 x 4) whereas the donor PSU only has a 4. Should be enough power if the mobo is OK, but no idea whether the mobo is designed to only work with 8 pins.

Tomorrow I'll try to power the donor machine from the failing PC's PSU (too fed up now).

It happens sometimes. 3 years ago I built up a new PC to replace my ageing system (7 years old, so had served me well), however I decided to keep the beefy 850w Corsair modular supply from my old PC for use in the new one. New PC was built up, I was steadily setting it up, then after 2 days there was a loud bang as the PSU decided to give up the ghost in rather spectacular fashion.

Thankfully, it didn't damage anything when it blew and a new PSU resurrected things. But yeah, can be a shit when things break like that :(

I'd just (a couple of months ago) built the whole lot into a new case taking time to cable-manage properly. That means that it's all tightly routed with cable ties behind the motherboard. Bit annoying to have to pull it all apart so soon.

I suppose, looking on the bright side, if the PSU is OK and it is the motherboard that's given up, at least I have a decent PSU for the new build.

If the worst comes to the worst, any idea of an AMD CPU which will have similar or better grunt than an old i5 4960 (which was clocked at 4.2 GHz)? I'm thinking of a Ryzen 5 3600. 

The Ryzens should be pretty good. Not sure how they compare to your previous CPU mind you, might need to check a few reviews.

For my last build it was pretty straightforward as my old CPU was a 1st Gen Core i5 750, so pretty much *anything* was faster!

My idea about a Ryzen 5  was based on about 30 seconds research round about when I bought a new case. That purchase was inspired by an earlier opening of my ancient Antec case to (finally) investigate what had been rattling (tiny piece of card got into a fan) and thinking how ghastly it was. 

I'll have to do a bit of reading. But hopefully not - as I'm actually quite happy with the i5. Knowing my luck, both mobo and PSU will have gone together.

Well, the PSU seems OK having successfully powered up my Plex/backup box without any complaint (apart from me moaning as I threaded the 24 pin connector through a rats' nest of wiring).

So, last try before I give up and spend more money is to strip down and rebuild the PC to rule out any accidental prods and tweaks from installing the new card earlier*. I have my doubts. I think it's probably a failure on the motherboard. It could be the CPU I suppose, but that means replacement anyway.

25 mins later, failed to POST basic configuration with CPU, cooler, 1 DIMM, 1 boot drive...and that means replacement :(

I suppose building will be quite fun once the spender's guilt has died down. I suppose I could ebay the mobo and CPU as "one or both not working". The GA Z97X working goes for north of £100 which is stupid money and the i5 4690K for around £60.

AAARRRRGGGGHHH!!!!!!! BOLLOX to this computer shit! So I unplug front USB and sound and swapped one DIMM for another. It POSTs and goes to a "previous boot failure" screen. This makes me wonder whether the new NVME drive has failed. Before I do anything, I just power off and power on. No POST. So just out of curiosity I remove the NVME drive. And yep, this time I get a "missing boot drive" screen. So I power down, add a USB mouse and keyboard, and power on. No POST. Power off, take out mouse and keyboard. Power on. "Missing boot drive" screen. So I add the mouse and keyboard back and hit reset. This time I'm able to get into the BIOS. Load defaults and restart. No POST!!!!!

My best guess is a fault like a broken solder joint. One last strip down and rebuild tomorrow, and a check of the motherboard and everything else really, for anything obvious
 
*and the original, and a GT710 in a x1 slot

((((WmA)))) An intermittent fault is the worst. It could still be an inadequate or dying PSU, managing to boot a less power-hungry system, but falling over as the more demanding one boots, and the failure expressing as a failure to adequately power various components more or less at random. A new PSU isn't the most expensive item and it sounds as if it could do with replacement soon even if it's not, ultimately, the guilty party.

Although your symptoms aren't anything like they ought to be, it might also be worth swapping out the BIOS battery, if only because it's cost-free.

Have you tried to see if it will post without a drive in? Sometimes the SATA addressing can get messed up (my fanciful attempt at an explanation), and if you move the drive to another plug on the MB AFTER posting with no drive connected. Anyway it worked for me once or twice for hdds on two different-gen mobos. Maybe it makes the bios reset, I dunno, I'm more of a trial-and-error type of fixer.

I put a new battery in when I changed the case. And, yes, I know it could still be the PSU :(

It successfully powered my other PC though, which is fairly well loaded with components - i7 with loads of drives. 

Yep, tried it with no drives. Booted to the BIOS once then failed to boot when I turned it off and on.

OK - had another go with a totally rebuilt, minimal, PC. Still no POST. Swapped the PSU into the Plex server again and it works perfectly.

Off to PCpartpicker!

Just to complete the story, I am now chugging along with a Ryzen 5 3600, MSI B550 Mortar, EVGA 1660 Super, and 16GB of Corsair Vengeance 3600 memory. PSU still holding out.

Very nice!

I haven't dared to look at my bank account recently.

I got a discount on the mobo by buying from Amazon "used but as new". Well, it wasn't exactly that, because some dickhead had rammed a front USB plug in, probably backwards, so the pins were pointing all over the place. Probably the reason it was returned. Once that was fixed it was fine. 

I do feel like I'm behind the times though, since this is the first fully graphical/UEFI BIOS I've had. My last board had a dual view, but what could be done through the graphical view was limited compared to the trad menu system. All this memory profile malarky is new to me. I'm sure I'll get the hang of it.

 

Had the exact same experience building my current system. Things have moved on a long way since my Core i5 system from 2009! Saying that, I guess one the reasons why it seems a big change is just because of how long systems last for these days.

Rewind a chunk and it was typical to pretty much replace a PC after 3-4 years, nowadays it's not difficult to keep a system going for 8+ years with a couple of minor upgrades here and there. Hence when we do eventually do a full replacement, a lot of things have changed in the meantime.

Glad you're up and running now.

Thank you kindly. 

My heart sank a bit this morning when my Plex box was missing from the Network. It was hanging on the restart from a recent Windows update with a message that the memory had decreased "Press F1 to continue or F2 for setup". Sure enough, only 8 of 16GB showing. I pulled all the sticks out and reseated them, which restored the full amount. Hopefully that's it.

Those of you waiting on the least bit of news from me (which not even I do) will be delighted to know that I got in excess of two more years of service from the PSU mentioned in this thread. It is now totally defunct, failing paper clip and multimeter tests. Seems to have been killed by a very long run of FlowFrames, a video frame interpolation app which uses GPU, CPU, Disk and RAM intensively. It probably lasted for over two hours of this and suffered numerous similar insults in the last couple of weeks. I'll be interested to see whether it actually finished when the new PSU arrives.

Had a work NAS fail unexpectedly a few weeks back. Not a drive issue (the 4 RAID drives in it are probably fine); a 'zombie' celeron/chipset (LPC clock) issue we were never notified of. Luckily this was our formerly main file server that had been relegated to backup use several years ago ... I look at these devices differently now.

That all looks a bit complicated to me. I just bought a new PSU which should arrive tomorrow. There's a sorry looking pile of snipped-through cable ties as well. Doesn't hold the same excitement for me as building PCs used to have. I did (briefly) consider buying a PSU from a local PC shop, the kind of place where they still offer advice on how to set up your config.sys and autoexec.bat. Then I saw how much their cheapest PSU was. Sad really.