Can't join any server, nor host my own game

I can't join anyone's server, this message keeps popping up for EVERY server I try to join. The servers I tried to join were being used by other people normally, only I got the error message.

I can't even start my own world, as the game stays on the loading screen forever.

Reinstalling the game didn't work, neither 32 or 64 bit version worked, disabling client mods didn't work. I don't know what else to do.

Please send help