our server was attacked by a DDOS attack. Our serverip was disabled for 2 days.

Now I've some problems to stay connected to my Server. It seems to be that I'm the only one who has this kind of problems.

I can connect for 10-30 minutes then I receive a connection lost for at least 30 minutes.
When I connect to other Teamspeak server everything is fine.

I can ping my server and can connect to my Server via ssh and scp without problems
The iptables of my Server are clear.

I also installed a fresh version of teamspeak without luck .
To Connect to the Teamspeak server I have to wait at least 30 minutes or
if I restart the Server I can connect instantly.

ServerDistro: Ubuntu (lucid)
Client: Windows 8.1 64 Bit

Has anyone an idea what happend and how to fix it?