Sudden Connection Problem

I know I know, I've read the other threads on this topic, but I'm a bit of a noob and would need step by step instruction. I get the server closed connection message. I switched into active mode as opposed to passive. The thing is I have been using SmartFTP for almost a year with absolutely no problems, then suddenly yesterday it quit on me. I have not downloaded any new firewalls, and I have even disabled the built in XP firewall. I have checked and rechecked my username and passwords. Any suggestions?