In the last few weeks, my PC (self-built) has started exhibiting the behaviour given in the thread title. It could be switched off and dormant for hours, then just turn itself on. It might get all the way to the login screen, it might get to POST then shut off, it might get past the BIOS diagnostics entirely, then shut off and power on again. Doesn't appear to be any logic behind it.
If I do get it up and running, I might be using it for 1 minute or 10 hours then it might start an orderly shut down. No BSOD, just as if I'd initiated it. In fact, if I open up a brand new document and type something to prevent it shutting down immediately for fear of losing work, and cancel the shutdown procedure in time, event viewer claims that my user login initiated the shutdown. I didn't. But something did.
* BIOS temps are normal and well within range: 20-50 degrees max (I'm no gamer). And most of the problems stem from it starting up cold.
* BIOS settings for WOL, ACPI etc are unchanged from normal (i.e. off or S3, etc).
* I'm not using hibernate.
* I've systematically removed each piece of hardware - graphics card, sound card, SSD, HDDs, DVD burner, USB devices, even the LAN cable in case something was triggering it to wake up (there's no Wi-Fi connection). Each time I've left the system powered down, and it'll spring to life after some time - from seconds to minutes/hours after it's been shut down from Windows.
* The only change I made recently was to introduce a new USB keyboard after my last one gave up. Thought maybe it was tripping it into some 'power off' state or one of the soft keys might be malfunctioning and causing the PC to wake up or shut down. Unplugged the keyboard: no dice, PC still misbehaved.
So, after pretty much ruling out software and most major hardware components, I'm left with basically three pieces:
* Case switch shorting internally somehow triggering power on/off.
* PSU fault triggering power on/off.
* Motherboard fault.
I've dreamed up the following tests that I intend to try soon:
1) Disconnect the power/reset headers from the motherboard. If it's the case switch malfunctioning, the PC will behave itself without these switches connected. I can short the power pins or wire up a temporary switch in the meantime if I want to power it on.
2) Try a different PSU if I can lay my hands on a spare unit.
Is there anything I might have missed in my diagnosis so far? Anything else I can try? Thanks in advance for any information or advice.
If I do get it up and running, I might be using it for 1 minute or 10 hours then it might start an orderly shut down. No BSOD, just as if I'd initiated it. In fact, if I open up a brand new document and type something to prevent it shutting down immediately for fear of losing work, and cancel the shutdown procedure in time, event viewer claims that my user login initiated the shutdown. I didn't. But something did.
* BIOS temps are normal and well within range: 20-50 degrees max (I'm no gamer). And most of the problems stem from it starting up cold.
* BIOS settings for WOL, ACPI etc are unchanged from normal (i.e. off or S3, etc).
* I'm not using hibernate.
* I've systematically removed each piece of hardware - graphics card, sound card, SSD, HDDs, DVD burner, USB devices, even the LAN cable in case something was triggering it to wake up (there's no Wi-Fi connection). Each time I've left the system powered down, and it'll spring to life after some time - from seconds to minutes/hours after it's been shut down from Windows.
* The only change I made recently was to introduce a new USB keyboard after my last one gave up. Thought maybe it was tripping it into some 'power off' state or one of the soft keys might be malfunctioning and causing the PC to wake up or shut down. Unplugged the keyboard: no dice, PC still misbehaved.
So, after pretty much ruling out software and most major hardware components, I'm left with basically three pieces:
* Case switch shorting internally somehow triggering power on/off.
* PSU fault triggering power on/off.
* Motherboard fault.
I've dreamed up the following tests that I intend to try soon:
1) Disconnect the power/reset headers from the motherboard. If it's the case switch malfunctioning, the PC will behave itself without these switches connected. I can short the power pins or wire up a temporary switch in the meantime if I want to power it on.
2) Try a different PSU if I can lay my hands on a spare unit.
Is there anything I might have missed in my diagnosis so far? Anything else I can try? Thanks in advance for any information or advice.
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