Hey guys I know this is a long shot but maybe someone could help

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Hey guys I know this is a long shot but maybe someone could help me out I have tried googling but I can't figure out exactly what's going on.

So, a few months ago my PSU died and i replaced it with another one. Ever since then what happens after i shut down my computer and turn off the switch on the back of my PSU is that the LED light turns on like once in every X seconds which would indicate to me that there is some sort of residual electricity charge or something on my motherboard. I am unsure if that is the case and how I should go about fixing it, I have replaced all the rams and even the battery chip but the problem persists. Recently my old GPU finally died (8800gt) and my concern now is that this "blinking-LED" issue could damage my components so I'm afraid to order a new 150-200$ GPU just to have it be susceptible to damage by a charged motherboard. Keep in mind that having a charged motherboard is what i suspect is occurring but I have little to no understanding on this issue and would appreciate any kind of help. Also keep in mind that everything has been working fine ever since i replaced my PSU, I just ignored the blinking-LED issue and I doubt it ruined my GPU since it was pretty old and used up anyways.

tldr: My motherboard LED blinks when all power is off, how do I check if it's safe to install new hardware on this computer?