[CLIENT] Can't log in! Black Client?

When running LoL, either normally or as Admin, I hit "launch" and it goes to load the login screen. However, it gets stuck and instead of the login screen, the client is black. It stays like this indefinitely. Frequency is 10/10. I have attempted a repair, to no avail. This is the first night it's happened, although I was able to log in and play after patch 4.21 ONCE.