League Client (before log-in) won't work... help!

League won't load. It's pre-login, right when you open league

I'm positive that it's not a connectivity issue, because it doesn't work from the school WiFi or my own WiFi at home. I get a black screen and nothing will load-- league worked fine yesterday, even after updating. Today when I opened league, nothing!

If anybody has experience with this issue, please, lend me your knowledge!