Can I have IT on the plane as carryon? :)

Why can't you just put them in your hold luggage?

Edit: Pack them properly so they don't get destroyed then. Wrap them up safely.

if you have the box that they came in just put them back in the box and put them in your luggage, they go through a lot worse in shipping then they will under the plane just put them in the box and between your clothes they will be fine. They might give you trouble bringing it on the plane. They dont like you having anything you wont need to be using during the flight.

I don't know, before I carried my 21" monitor as a carry-on. I know its stupid, but I don't have any space anymore.

I just said it's too "fragile" to be in the baggage. I just wrapped it carefully (put comforters), and put it in a big bag(which was supposed to be a coat jacket cover)

A friend had no problems bringing his Acer notebook as carryon (GER - USA and back), but you should also bring your receipt, so you can proof at border control that it's yours and when/where you bought it.
In Germany you would have to pay tax for expensive electronics if you can't proof that you already owned it before your trip.

Ive never had an issue taking my laptop with me as hand luggage

There shouldn't be any problems. There's no security measures in the US restricting computers being brought as carry-ons. Otherwise it's the airline's policy. All major US airlines allow one carry on and one other item, which can be a laptop, purse, etc. I doubt you'll be able to use your mouse during the flight just because of space issues, but if you're just wanting to keep it safe there shouldn't be a problem.

No you can't. You see, the same question a leaellynasaura have asked before and he didn't listen to the advice of a pterosaur in charge of flight security and took with him his iStone. During the flight, his iStone interffered with the trajectory of a giant asteriod that caused to deviate from his peacefully course and heading to the Earth. And after that we all know what happened. So if you want to play with Mother Nature and Karma you can take your mouse and keyboard on hand luggage.