I have been dealing with this issue of the screen fading to black for the past month now, and it started right at about the year and-a-half mark of using this phone. It's pretty upsetting when I still have 6 more months left on my 2-year contract to pay off this phone, and the problem is some sort of hardware issue with the motherboard (Or at least that's my assessment after reading this thread). After following this thread for the past few weeks, I finally decided to give my input/solution to see if what I did to my phone possibly works for anyone else.
I don't know if anyone else has tried this or not, but I did this and my phone has been working perfectly for the last 4 days in a row after getting progressively worse (putting paper next to the camera and over the battery seemed to help a little, but then after a week, my phone was barely working at all). 5 days ago, In the developer options I changed the, 'Background process limit' setting to 'At most 1 process' for one day, and then I changed it back to 'Standard limit' the following day. This seemed to drain my battery the day I had it set to 'At most 1 process', but the next day I changed the setting back to 'Standard limit', and my phone started working completely normally again with no issues.
I waited a few days to post this to see if the problem started back up again (I've been dealing with this for an entire month), but so far so good. This might not be a solution for anyone and maybe my phone started working for some completely unrelated reason, but I thought maybe someone would want to try it, as it is pretty easy to do. I had 2 pieces of paper in my phone for the last couple of weeks, but it didn't seem to make a huge difference. When my phone started working 5 days ago, I left the paper in my phone, just in case if that's what was helping, but today I took it out. I'll post again if anything changes, but as of right now, my phone is still working. Hope this helps someone!