My phone freezes :(

Hi, i have a SGH-I337M, with the AOSP 6.0.1 rom with root, since i can remember the phone had been pretty much hot, i didn't care much back then since i use it a lot but recently my phone started to freeze, like the screen freezes and i cant do anything, not even turn it off, so i have to take off the battery let it cool for 20 minutes and start it again, then it works about 10 or 20 minutes and then again it freezes i think it might be related to the heat. Also some few times my screen has turned green and then white and others few times i can see some sort of colored strings.

I'm pretty sure its hardware related but i don't know why it happens and if it can be repaired, do think ill have to change the whole motherboard?

Thanks in advance :D

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