[help] overheating

Good evening everyone, I'm really in trouble, I have an exam tomorrow and I can not run my LED matrix. please I need help immediately!

I have mega Arduino 2560 with an external power supply from 7.5V, and above it says (PRI: 100V-240V ~ 60/50Hz 350mA SEC: 18V 1500mA 3/4.5/5/6/7.5/9/12V) to connect a perforated board 28 series resistors connected to GND, the resistors are 220-hom. and on the other hand there is 5V. this is attached a button that illuminates a LED and a cable that goes into a pin of Arduino. my problem is that I have 28 buttons / LEDs, and they attack more than 4 of the Arduino board is really hot and I'm afraid to melt! I attach a picture, I hope is clear.

I hope is clear.

Sorry not much of that makes any sense.
What is getting hot?
Do you have a schematic, not just a silly practical layout?
It looks like you don't have a series resistor in line with the LED it appears to be shorted out with a wire.

Unfortunately I am not able to draw a diagram. all I could do is make a layout like that. I can redraw it better. I do not know what else to do. I ask you kindly explain to me why you say that there is a short circuit

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the part that gets hot is the square at the center

Unfortunately I am not able to draw a diagram.

Why not? Pencil and paper then photograph it.

I can redraw it better

It needs to be how you have it.

You need to describe what you have, that explanation was full of jumbled up words that made little sense.

Is the connection to the arduino board an input or an output?

I ask again what is getting hot on the arduino board.

Are you sure you are feeding it with 7.5V, have you measured it?

here's a drawing I did of my project, which will then be multiplied by twenty-eight. I believe that this image will explain it all. if there is still something unclear please tell me what. (voltage is 7.5V)

This is not a very conventional circuit.

I ask again, is the arduino pin an input or an output? All pins connected to this must be inputs. If any pin is an output you risk damaging the baord.

If it is an input then I can't see how this will work because when the LED is on there will be a voltage on the input that will make it look like a logic 1, when the LED is not on the arduino pin will be connected directly to 5V.

For how to combine an LED into a switch the see this project:-
http://www.thebox.myzen.co.uk/Hardware/Pendulum.html

what you said is right, I took the test in reverse. and if I press all 28 buttons. the chip does not heat up more, or rather does not heat up much. What should I do? I would be fine also the solution to remove the leds, and only use the buttons. I looked at the tutorial that you gave to me. I feel stupid, but I can not understand

What should I do?

Wire up your switches, resistors and LEDs like this:-