My Folding PC has been sitting all alone this week with no monitor, mouse or keyboard while I've used them to look at a friend's PC. I've just plugged them all back in and nothing came up on the screen.

I rebooted the PC and it is switching on and then off and then on again of it's own accord. The time it is on/off is NOT regular. I've shut down the PC myself, only for it to boot of it's own accord a few seconds later. Surely this has to be PSU???

I've tested the PSU with a proper PSU tester and simultaneously a multi-meter and all the rails seem fine (there is no 12V2 on the main ATX connector)

There are no BIOS beeps even with the graphics card removed. As long as the power is on, the DVD drive keeps spinning up, motherboard fans are working, but I'm not certain that the HDD is spinning up (they're so damned quiet these days)

I don't have a spare PSU at the moment as it is sitting in (another) friend's PC proving that his was goosed (which it was) so I need to hurry up and replace his PSU before I can check this system.

It's another new fault for me. I've had systems switch off before, but NEVER back on by themselves!!

Thoughts welcome once again. Thanks.

Updated- Checked that PS2 connectors hadn't got bent pins- I've had this problem once before and have checked that the reset and power switches aren't dodgy by disconnecting them.

More testing shows that power switches off then on after about five seconds. DVD drive will spin up anything from once to about four/five times before power goes off. Clicking occurs from PC speaker, but no beeps.

I got past POST once but once only after leaving it without power for a couple of hours.

My PC was switching itself back on even when I did a manual power down (held button in). I'm sure my BIOS wasnt set to restart on power failure or anything so I was puzzled. It was since installing a new GFX card. I removed the power, performed a full BIOS reset then it was fine.

Nothing has changed in the PC apart from removing the peripherals.

It is an inexpensive (not cheap!!) Hiper PSU and it has been on almost constantly for 12 months now folding. It isn't the best PSU in the world, I know, but it is 530W and the only power-hungry component in the whole PC is an E6600 CPU. I suppose that being on for that long might have led to failure- although it shouldn't of course.

I've left it off all night with the BIOS battery out, but nothing new this morning.

I've got a Corsair PSU in mind for my friend's PC (Custom PC approved) so I'll get on with sorting that out so that I can have my spare PSU back and test my rig.

I've killed loads of hiper psu's.
They don't seem to last that long, probably explains why they went bust.

Thanks, saspro.

I would have ID's the problem already if I had the means, so anything to think about in the meantime is welcome.

I went for Hiper as it still worked out at the mid-range price of £10 per 100W, and as it was hard to find low-powered (<600W) PSUs for my basic system. However, if they are known to be dodgy, then 12 months of constant load could well have killed it.

Just an update.

It seems that it was the PSU. I've tried my spare one and the PC booted three times without any problem. I'm not sure if it was some sort of problem with the circuitry that gets the OK from the system as all the voltages are stable. I might keep the PSU as a second supply for any system or parts that I'm playing around with if that's the case.

Now, the bad news. Because my (currently) spare PSU is a big Tagan Dual-Engine, it won't fit in my early ATX case as it stands, so I need another new PSU.

Ditto, built a handful of PC's about 4 years ago for friends all using hiper PSU's and I've had to replace all of them.