I have almost the same problem as in Delay before booting?
My computer is a practically new (couple months) Lenovo X200 Tablet (System Model 7449FXG).
So when I press the power button, the indicator light that means "computer is on" turns on, but nothing else happens for about 5 mins, after that the computer starts booting normally. The same happens also on restart. And no USB or any other device for that matter is plugged in to the computer. And at the delay time the monitor is blank - actually not on at all.
I ended up giving my computer to local IBM / Lenovo Service and they replaced the mainboard. They did not check (or did not want to tell me :) ) what was the exact cause of the problem though. But I am happy that my computer boots up normally again :)
Thanks for all your help.