HDTV Invalid Format due to playing on Fullscreen.

Yesterday League worked totally fine without any problems, but out of nowhere today getting into a game I got a problem where my monitor (LG HDTV M1931) would just black screen and it would say "Invalid format". I read about it and it may be because the monitor does not support the applications' resolution. I both use and play on 1366x768, Screen refresh rate: 60Hz. I'm confused to why this keeps happening, why can I play the game on Borderless and Windowed Mode, but Fullscreen just doesn't work for whatever reason (I hear the sounds of entering the game, reconnecting, moving etc. but can see only a black screen and I'm forced to Alt+F4 the game). How is such a problem fixed?
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