You have been answered repeatedly but you do not understand the answer because you do not understand the mechanism of the OSI model. If you were to search a tutorial (as has been recommended) and read it through carefully you might have a better understanding of the OSI model and therefore, understand the answer.
I would highly recommend you talk to your instructor and ask him/her for some extra time of theirs to give you extra instruction.
Also, have a look at the following OSI chart in .pdf format (use controls at bottom to enlarge page so you can read it):
This is such a terrific chart, I got my boss to order a full sized one for me just because I like it so much and I have it hanging in my office.
Take a look in the orange section under "Routing/Switching Protocols" down in the "Network Layer" (layer 3). Notice "IP" is there. IP as in "IP address"
You keep saying the network layer is not involved and you've been told multiple times it is. Yet you keep insisting it's not. Well, the above chart proves conclusively it is indeed involved.
Since I know you're still confused I'll attempt to explain by adding on to what others have said.
You've had it pointed out to you that when you connect two computers together using a network cable...........regardless of whether or not it's a crossover cable going PC to PC, or in patch cable running to a switch...........in order to have communication, both PC's involved must have a valid IP address within the same subnet.
Take two computers and a crossover cable. Plug them in. Then try to copy a file from one to the other. You can't. That is, you can't until you give them both a valid IP address within the same subnet. Then, and only then, can they communicate with each other.
Now, if you still don't get it..........there's nothing else we, or anybody else in this world can do to make you understand and we're back around to the original point that you don't get it and need help learning it.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.