[maddinat0r]

The network thread is frozen, that's why you get a download rate of 0.0 KB/s and that's also why everyone has that AFK icon. If you can't execute any gamemode command, then it's likely that this is a physical server issue (no warranty). Maybe some other program on that server is taking all resources? That would be the most likely cause.
But it could also be, that the gamemode is somewhere in an infinite loop. You would need some really bad code to cause such a huge lag.