My TV (Samsung Smart Tv 32Inch UA32M5500ASXNZ) has recently started doing this thing where the screen randomly goes black, while sound still works. When I turn my TV off and on again, the screen works as before. How long I off it for doesn't matter- it works even if I turn it off and then immediately turn it back on.

Once on again, it will work for a few minutes (3-7mins, and then will fade to black. I've tried doing a soft reset and changing the power cable, but to no avail. I've also checked the timer and eco sensor and turned off the automatic dimming in case that was the issue, but still nothing. 

The screen has also had 2-3 flickering lines on the top and bottom of the screen for a few months now, but that seems to be a non-issue. They're very fine so it doesn't really cause much of a hindrance while watching stuff.

When it blacksout, there is still backlight, like a normal black screen (not as though the TV is off), but I can't see any color when I shine a torch to the screen. This started around 4 days ago, it randomly worked fine for 2 days after the first day it started acting up, and now it's back to blacking out.

Any advice on what the issue could be, and how to fix it?