Dude same thing happens to me too, I have a 5220 with same issue, regardless of operating system: had vista, installed 7 with no luck. When powerd off, I plug in the charger, nothing, it's dead - no light whatsoever. I unplug the charger and it boots up only at the second / third press of the power button.
I posted somehow the same question yesterday but still no replies. I hope it's not the mobo.