[help] server down/flood/bots

Hello guys. I have a problem on my server. Someone came on my server and he said "the server will be down". And after that the server is down. I don't really know why, but i check server_log.
I think it has flooded my server or he added bots or something with his IP.

It might be because of this? : https://www.youtube.com/watch?v=sdJk...ature=youtu.be


If someone know, please reply.

P.S: I know about mysql errors, I've solved them.