How would I go about fixing or repairing an Xbox One S that seemingly cannot output...

Recently my friend gave me their Xbox One S, because they said the console stopped working and the display didn't output anything. They thought I might be able to fix it so they offered it to me and I took it, and I figured out that the only way the Xbox will show any output is if I start it in low resolution mode in which everything works perfectly fine, aside from the resolution being set to 640x480. Basically, the Xbox does not output anything in a resolution above 640x480p. I have tried factory resetting it many times, using different cables and even different screens, (TV, computer monitor), and nothing seems to make any difference. I was wondering if there was anything else I should try or is it just best to send it in for repair?

TL;DR, My Xbox One S seems to only be able to output a 640x480 resolution, and I was wondering what I could do to fix this.

:)