Today my PC has shutdown twice randomly. We’re talking going off just as if there’d been a power cut.
When booting back up again, Windows doesn’t say anything about shutting down badly.
I’m not sure it’s heat because checking BIOS at the boot up, temps were 27C and 25C.
And Speedfan shows this:
HDTune shows no errors on either of the the hard drives.
I’m at a loss of what else it could be.
EDIT:
Memtest passes fine as well.
kinda hoping that 12v reading is speedfan and it’s normal inaccuracies … if not, your psu is on the way out.
DT.
Using HWMonitor gives this
which looks far better to be honest!
The voltages show fine in BIOS as well.
If it was the PSU, I’d expect it to shutdown when it draws more power, ie I start a game or something but this went the first time whilst I was backing up a Steam game to USB and the second time when I was running a defrag.
so both shutdowns when the HD is being used ??
Yes. Though HDTune shows no errors.
I’ve already got a drive on it’s way to replace the IDE drive there (which Steam is installed on) and was the drive being defragged (should be here Monday - eBuyer made damn sure I got it on the 5th working day 
)
I would have said PSU, but my second choice would be memory. I’d run MEMTEST86 on it overnight to be certain that isn’t the problem. Also, take a look at the motherboard and make sure none of the aluminum electrolytic caps are starting to “popcorn”.
Egad’s suggestions are my first thought too.
Memtest has run fine (well one pass).
Overnight isn’t an option (it’s in my bedroom and I need to sleep!) but I’ll put a Memtest on during the week whilst at work. I’ll check the board when my hard drive arrives.