Phone cannot boot at all

So I got a bit of experince with the different boot modes in Android, the different key-bindings etc.

Anyways further on to the actual question/problem, so last night I but my phone next to the bed on the floor, while it was connected to the charger, as I always do. 5 hours later I tried to boot it on, it did not even get to the boot logo for the powering off, nothing happened. Tried to acces bootloader/recovery, none of those worked. Seems like the phone is completely dead. Even when I connect it to charging it doesnt boot up again. So my question is, which part of the actual phone is causing this? It isn't any software related issues, because then it would still be able to acces bootloader etc as that is seperated from the actually on going system. So what do I do? Anything possible? :)