Yes, reseating means disconnect and reconnect. Sounds like your BIOS is set to turn on PC automatically after power is introduced after having lost it. If you reconnect power switch, and PC starts working incorrectly again, I think you're right about it being the power switch.  They do go out from time to time, but not often.
My pc doesn't turn on after I plug it in and pressing the power button  
OPTIPLEX 3070 Sff no power