HELP! League Client will NOT open!

I have downloaded League probably 15 times and have not been able to open the client. Furthermore, i have followed virtually every instruction on how to open it, yet the only thing that opens is the logo, which disappears after roughly 8 seconds and then nothing happens. I have changed my DNS, downloaded the Hextech Repair tool, gotten rid of logs, changed specific codes in the files, but nothing works. It´s not the internet connection, as i have tried three different ones. Every other game works except for the amazing league client. Would appreciate an alternate method to resolving this problem. Thanks!
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