Question; In the League of Legends > Config folder, open the game.cfg file in Notepad. Do the following lines under [Floating Text] have 1;
[FloatingText]
EnemyTrueDamageCritical_Enabled=1
EnemyMagicalDamageCritical_Enabled=1
EnemyPhysicalDamageCritical_Enabled=1
TrueDamageCritical_Enabled=1
MagicalDamageCritical_Enabled=1
PhysicalDamageCritical_Enabled=1
ManaDamage_Enabled=1
ManaHeal_Enabled=1
Experience_Enabled=1
Debug_Enabled=1
Absorbed_Enabled=1
OMW_Enabled=1
EnemyCritical_Enabled=1
MagicCritical_Enabled=1
Critical_Enabled=1
1 means on, 0 means off. This is an obvious fix to save the setting, so I'm sure it was suggested in the threads you read about it, but I want to make sure.