Screen completely black apart from cursor

Queued for ranked, got through champion select perfectly fine. Screen then went black (which, at least for me, is normal for a second or two before the loading screen comes up). Cursor appeared, but no loading screen - game definitely loaded because I could hear normal game noises.

Tried disconnecting and reconnecting, switched monitor, reset my computer and tried reconnecting - same problem again and again, so was forced to leave the game :(