There are 3 possibilities here:
1. You are connecting to fake servers. Try connecting to "DonkeyServer 5". But watch out, there are fake ones called the same, I can't tell you the right IP address now since I'm not at home.
2. Your ISP is blocking ed2k traffic. Try to change the port number you are using via the preferences menu. If this doesn't work it's most likely that your ISP really blocks p2p traffic effectively and we have no solution for this yet.
3. Use KAD. This works just as good as ed2k servers to get the necessary sources.