I'm not a world renowned expert in hardware diagnosis, but recent experience has told me that very often, intermittent faults will be memory problems.
Or so I thought.
When I say 'intermittent faults', I mean freezing desktop or applications, blue screens or the machine will simply reboot itself with no warning.
Or just switch itself off, which is my favourite.
So, on a recent problem machine, I had discounted almost everything through trial and error although you can never discount the motherboard itself, which is definitely NOT my favourite.
By pure chance, I changed the HDD sata cable on this machine and the problem went away and I am pretty sure, not to return.
And it's not the first time I've come across dodgy sata cables.

Cases?
Well, I've recently been building some new PC's and a recent case came with a bottom loading PSU.
I've had a few bad experiences with this design, mainly because most motherboards have the 4/8 pin 12v cpu power connector at the top of the mobo, near the io shield.
If the psu cables aren't long enough, you end up scratching your head and wishing you'd never started the damn job.
On another occasion, the case itself had front panel connector leads that weren't long enough to reach the front panel connectors on the mobo.
One could say that it pays to do the research first, but sometimes you can only discover these foibles when you mate everything together, so to speak.
So when the customer says he wants the Supercharger mobo, with a bottom loader, you just have to cross your fingers behind your back.