?? There are several various ways to hack on's computer. If you typed in simple keywords in Google or a different search engine, it'd tell you how to hack someone's PC/Laptop while it being off.
The result? You'll just have problems turning it ON. So it'd actually be better if the computer was off to hack it. :3
Why would one act like he knows so much and not do anything? That's retarded. Of course I know what I'm doing, if I didn't, why would I have started all this?
It's simply not possible while the machine is off you just can't hack it.
You can gain access to a computer when it's "Off" I believe if it has wake on LAN, however, don't quote me on that because I am not sure and too lazy to check. Regardless it would require being on the same network.