Power issue with the motherboard P35-S3L

Power issue or the motherboard issue

Hello
Not sure where to post this so I'll put it in here. I've been building new computers for a while but i still get the occasional problem that is new to me. Just built a new system and all seemed easy enough, but after plugging the power in, yet before i pushed the power button, the power LED came on and the system fans started working.I also noticed the monitor flashing too! I was too scared to push the power button in case i fry the whole thing. Can't find any mistakes please help!
 
Found the problem, the internal card reader was being over-powered, amazing how something so small can cause such a worrying issue.
 
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