In my opinion, the main mechanical failure risk in a computer is the hard drive.
Generally speaking when I think of a PC failure... I also think hard drive first. But when I worked as a network admin with responsibilities for PC selection, purchases, and software (as well as network) for a small government office. I also had failures due to power packs, processor fans, bad motherboard capacitors, and even most commonly... update errors.. that disabled desktop computers.
I like the idea of a small Home Automation laptop...
or maybe even a touchscreen tablet that hangs on a wall. But as cheap as computers have become... I still think Home Automation can be the best use for those old desktop dust collectors. I am using an old P3 that I rescued from landfill.. loaded XP on it and bumped up its memory with RAM I purchased [used] from a flea market.
Don't get me wrong... it's not that I am all green minded. I am cheap... and on a fixed income. But with a little effort... and knowhow that can be found on-line... just about anyone can have world class Home Automation using PCs that are regularly set out curbside on trash pickup days.