I will be taking my laptop in my hand luggage when going to the US. While returning, I will be bringing a new iPhone 7 Plus from the US with a power-bank charger. Is it OK to bring them in boxes in my hand luggage? Do I need to do anything or is it OK to bring them like that?
Yes, you can bring all three (the laptop, smartphone and power bank charger) in your hand luggage. The fact that they are in boxes will not matter.
Passengers are allowed to take personal electronics on board, provided they fit the airline's weight and size restrictions. These items include laptops, personal audio systems, hand-held gaming devices and digital cameras. It can be safer to pack these items in your carry-on luggage, reducing the risk they might be lost, damaged or stolen. Most airlines place restrictions on passengers using electronic items during take-off and landing, but passengers are allowed to carry them in their luggage at all times. Source
Please note that the TSA requires you to take the laptop out of your bag while passing through security. You can put it into the bag again after passing through.
Useful addition by @CMaster:
Note that you may have to pay some kind of tax when returning to Qatar. Check with the relevant Qatari authorities.