Whether you have disconnected all the boards and the problem persists, it seems to be a Power Supply (PSU) issue. Try to isolate complety the PSU and check a voltage. If it raises and suddenly cuts, the PSU has a bad component. I have experienced such an issue: when a component driving the tension output is bad,the current raises to much and upstream the system detects a short.
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If your computer refuses to boot or tends to turn off without warning, see the [https://www.ifixit.com/Wiki/Faulty_Power_Supply_to_Motherboard?revisionid=HEAD|Faulty Power Supply to Motherboard problem page] for possible causes and solutions.
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Whether you have disconnected all the boards and the problem persists, it seems to be a Power Supply (PSU) issue. Try to isolate completely the PSU and check the voltage. If it raises and suddenly cuts, the PSU has a bad component. I have experienced such an issue: when a component driving the tension output is bad, the current raises too much, and upstream the system detects a short.
Whether you have disconnected all the boards and the problem persists, it seems to be a Power Supply (PSU) issue. Try to isolate complety the PSU and check a voltage. If it raises and suddenly cuts, the PSU has a bad component. I have experienced such an issue: when a component driving the tension output is bad,the current raises to much and upstream the system detects a short.