Did you ever notice if it was blinking since you got it? If I had to take a guess, since the computer is otherwise completely operational, I'd say the wire that is going to the Power LED is incorrectly connected to the HDD LED pins on the motherboard. That said, the light would flicker along with hard drive activity. It that what it does?

Otherwise it might just be that the LED has a bad connection or it is about to go out. If it is too annoying and you can't take it anymore, you might be able to unplug the wires from the motherboard and make the LED not work at all.

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