Say you're sorry to whomever you upset on Warcraft?
There's really nothing you as a user can do about it. All the magic happens at the datacenter and in most situations they should realize it's happening before you do.
While khiltd is correct, you can also try some scripts that can assist it blocking a small ddos but most likely you'll need assistance from the data center.
mod_evasive can also mitigate issues where some idiot is simply running wget repeatedly to drive up your bandwidth bill, but a full blown attack really needs to be handled on the router.
If a reboot doesn't fix anything I'd file a ticket.
From SSH,
I used to run these commands.
service cpanel stop
service cpanel start
service mysql stop
service mysql start
service httpd stop
service httpd start
(I know I can do the restart instead of stop and start, but I found that sometime it doesn't work.)
Then as long as the ddos is not happening, the site should come back on.