Question Computers turns on and off

Oct 31, 2020
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I have a problem with my desktop computer (no brand, Asus motherboard p5qpro, intel processor, A-Open 440 Watt powersupply

When I started it up it continued starting up, shutting down in a split second and re-doing that every 5 seconds or so). Nothing on the screen, no beep, just restarting eternally.

The last time I used it (weeks ago, it also started eraticly and started Windows 10 untill the Windows waiting icon that stayed on. After very much rebooting with a long press on the on/off button, after 40 times or so, it finally booted and worked ok. I could stop it and restart it afterwards.

But today it didn't want to start and restarted all the time. I went though this forum and tried all the tricks I could find. I disconnected all auxillary devices and drives, but no solution. I finally unplugged the 20-pin lead to the motherboard and measured all the outputs. The all seemed ok (i put a metal bridge between a black and the green pin to measure it.). The grey cable came in at the requested 5 Volt.

I then changed the CMOS-battery. It tested 3+ volts, but changed it anyway.

I then reconnected the computer to the mains, forgetting that i bridged the green and black and that the large 20 pin connector was not inserted. Only a small 2*2 connector with 2 * 12 volt was connected from the powersupply to the motherboard.
The system had power, fans turning but no beep. When I pushed the on/off button, it booted, beeped, started windows, did a system update and worked perfectly.

I can shut the system down, but a small orange light on the motherboard stays on as well as the fans. Only if I disconnect the mains it stops.

If I connect the mains again, it gets power and the fans turn. If I then push the on/off button, the system boots and works.

So everything seems to work, but instead of using the on/off button I have to connect the mains, wait, push the on/off button and it goes. I stop it from windows and then have to disconnect the mains.

Any idea what is wrong and how to solve it?
 
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