hello aominedaikii, sorry to hear about your issue. Actually this has happened with me in the past, and i was as clueless as you are about the same.
i cant say what i am going to tell you is fixed workable solution, but i have done this and thereafter things have gone back to normal, that is game has started working properly
here is the things which i have followed:
1)downloaded the client in C:\PRO New Client
2)Cleared all temp files
3)uninstalled and reinstalled my gfx drivers
4)checked if any setting has gone wrong in firewall
5)Ran the Game as admin
this 5 steps worked for me, honestly firewall step you can ignore if you believe nothing has changed in it, others i recommend you to follow if you really want to try this way out.
Let me know if it works. Thanks.