[CRASH] Client 7.3 will attempt to load after Champ Select and fail.

I cannot play League at all. I have just been given a LeaverBuster warning because my pre-made would have to remake over and over. I've fully repaired the client twice and tried after each time. I've then completely uninstalled League and deleted all files to reinstall League.

Yet, when I after Champion Select finishes, and when the loading screen is supposed to appear, I get the League of Legends symbol that is supposed to appear only momentarily. However it does nothing and League of Legends becomes unresponsive. The client still works but reloading the game only brings the same crash.

How can I fix this? Repairing and complete re-installation has done nothing. Any ideas on what might be wrong? Thanks!