There might be any problem. If I were at your place, I would do the following -
1) Make sure that I can ping the remote machine
2) Check if there's firewall blocking the port on which ssh runs on both machines. If connecting via a proxy server, check if it's configuration has been changed.
3) Check if sshd is running or not on server
4) Check if I can connect to ssh server from any other machine.
5) Check if I can connect to the ssh server from the local machine.
ssh user@localhost -p portnumber
6) Check if any any changes have been made to