I need some arguments for both sides with support from the story if hamlet was crazy/mad or not.

Basically, give your opinion on why you think he was mad or not, and what he did to make you think that way.

and if possible start a discussion relating to the others' arguments

I think you can make a good case by going into how we define madness, and by different definitions people will come to different conclusions as to wether he really was mad or not.

I'd start with reading something like Camus' "Hero of the Absurd"
It's an essay dealing with the absurd, which is really where Hamlet fits in.
I'm not sure it will give you a definite answer, but it may add insight that's needed.
To be very very honest I've yet to read it yet, but I've had the intentions to as it was recommended by a lit teacher of mine in order to work on an assignment dealing with a character very similar to that of Hamlet