I use an old HP SFF office pc with athlon something, Ubuntu 18.04 for a home music & file server (MrsD.s old pc, she ran xp on it)... probably massively bigger than what you're going for, but free. It sits under my scanner so doesn't really eat up any extra space.

 :-D Yes, I'm aiming at about 6x7x4.5 inches. So a bit smaller. That said, my back-up PC is about the size of an enormous old desktop and has noisy Corsair water cooling, but it sits in the spare room so that's OK

There's a punk to New Romantic progression. A visionary manufacturer strips out all the fat and offers a refreshing barebones machine that challenges users. Then to build business they start to offer add-ons and new iterations with greater capabilities. Before long, it's just another machine with all sorts of gingerbread and bloat lashed on.  Then somebody has the bright idea of stripping out all the fat.

I prefer Bauhaus to Roccoco progression (I actually like both styles but, as I said, I've a low threshold of boredom).

It's the circle of life.

You say dumb terminal, I say thin client...

Just tuning in to say "Damn and Blast!"

I knew I shouldn't have talked openly about my backup PC. Went to look at the Plex server this morning and it wasn't there. None of the shares were available either, so with that sickening feeling so familiar to all home PC builders I went and looked at the box. Dead as a dead thing. Optimistically tried a new kettle cable but nada. Let it rest unplugged for a minute then tapped the on/off switch which produced a half millimetre twitch from the PSU fan. Unbelievably unable to lay my hands on a sodding paperclip right now, but it does look as though 3 years of running without a reboot has killed the PSU. As soon as I can confirm that, it's time to pray that's all that failed. May be time to invest in a new case as the present arrangement has got to be the shittiest ever with a PSU replacement involving a complete dismantle of the whole thing - it's one of those boxes where the PSU is inaccessible with a pass-through power cable to the socket at the back of the case.

Bah! Even more buggering bollocks. With a paperclip the PSU fan spins like a spinny thing. Now I've got to try and remember where I put my multimeter. Oh for the days when I had a couple of spare PSUs lying around!
 

MB fuse? Blown caps?

Possibly, and I am beginning to look at the cheapo no-name motherboard now.

So I hauled the backup PC over to my main desktop and hijacked the known working power supply from that. Yes, well. OK, the PSU started up as expected, but then there was a spark somewhere in the row of caps near the CPU power connector, so I turned things off.

Reassembled the backup PC with it's own PSU and wacked the power switch just out of curiosity. Damned thing started up, went through the bios screens and into Windows, but just before the desktop it shut down dead again. Beginning to think that all the twisting and turning closed a broken circuit (or something), or some worn-out caps gave it one last go,  but it didn't last.

So, I'll go over the PSU with a multi-meter and if the pins are providing the right voltages I suppose I'm looking at getting a new P55 motherboard.

 

Not the power-supply. All outputs within tolerance.

Now to see if I can find a socket 1156 motherboard with plenty of SATA ports.

When Mrs.D's sempron pc died, it was leaky caps. Oddly though only one ide channel was killed, otherwise it still worked, but we already got a replacement, which has since been replaced and is now the aforementioned music+file server on my table heaped with junk work area. The sempron got put out with the trash earlier this winter, after languishing under her desk for >5-years. I heroically desisted from cannibalizing its obsolete parts.

Why is that so hard? Why do I have enough brass motherboard stand-offs to interest a scrap metal company, my original PCI video card (128K of memory), two Matrox Mystiques, about 10 million completely redundant circuit boards including things that run scanners that no longer work with any operating system, a couple of CPUs from when people thought sockets were dead and riser boards were the future, and so on and so on? 

I firmly believe it's a man thing in that we're somehow wired (no pun intended) to accumulate potentially useful things that may well come back into some replacement role in the future, and when that eventuality comes about, we can rush to save the day by proudly holding up the decrepit equipment, shouting 'I told you it'd come in useful'.

I have box full of mobo screws, sata cables, molex connections, HDDs, old motherboards, random cable, chargers and more velcro and cable ties than you can shake a shakey thing at. I don't think I'll ever get rid of them. :J

Yep, never want to have the feeling of "I used to own that but threw it out".
But what also happens is "I definitely have one of those but I can't find it, so I'm going to have to order another".

Well, yes, exactly as I felt the other day. As recently as, ooh, only 3 or 4 years ago, I ditched a couple of old 250W power supplies which would have helped with my recent issue. Come to think of it they wouldn't at all since when I did manage to plug a known supply in the results were totally inconclusive. 

But there will definitely be a use for all those case screws, odd shaped devices for mounting odd shaped drives, ISA boards for 14K modems, CD Drives, that Iomega zip drive, those 21 Windows 95 floppies...'Good times, bad times, give me some of that...'

Well, I'm hoarding for the apocalypse, then I will either sell/barter this stuff for boots, beans and bullets, or I will build a mofo attack vehicle. Or maybe not... just in case, you know.

You should see the awesome quantities of shite I've accumulated in my home & in my studio, on the off-chance that it might one day 'come in'.

The apocalypse or Brexit, whichever comes sooner.

A pleonasm shirely? Aren't they one and same?