There could be a residual current in your motherboard, what you can do is unplug the power supply and hold down your power button on the case for 20+ seconds, this will discharge any current that could be causing the issue, if that doesn't fix your problem you may want to look into the condition of your power supply, also look carefully at your heatsink and check if the fan turns at all when you try to boot, if it spins just a little bit you may have a bad power supply, my advice is swap a couple parts and see what happens.
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There could be a residual current in your motherboard, what you can do is unplug the power supply and hold down your power button on the case for 20+ seconds, this will discharge any current that could be causing the issue, if that doesn't fix your problem you may want to look into the condition of your power supply, also look carefully at your heatsink and check if the fan turns at all when you try to boot, if it spins just a little bit you may have a bad power supply, my advice is swap a couple parts and see what happens.
On top of that check all connections inside the computer and out.