The first Cassandra db was be installed on my PC. The OpsCenter was launched and the first (test) node was created. But OpsCenter didn't work bacause agents failed to ssh to the node.
I got three suggested change in different settings to fix this. I did all of them and the issue was be fixed. My Cassandra runs on Windows 7(x64).
Add this line(s) (or update them) to the file below:
conf_location = C:\Program Files\DataStax Community\apache-cassandra\conf\cassandra.yaml (check the path!)
ssh_port = 2222
All the files can be found under the folder 'Program Files\DataStax Community'.