Ok so many people have had the same problem where your Launcher just simply doesn't start.
Check your avast Quarantine OR Virus Chest ("Scan for viruses" and then click "Quarantine" or "Virus Chest").
For some reason the 6.6 patch has freaked out Avast and it treats League of Legends like a virus.
Simply "Restore & Add to Exclusions List"
This may also be the case for other programs.
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