Hello, I'm a newbie in using postgresql on windows xp pro

Just a few days ago it was running and it was all ok, yesterday I found an error but I didn't make modifies before!

The error was
could not connect to server: Connection refused (<stringa in esadecimale>)
Is the server running on host "???" and accepting TCP/IP connections on port 5432?

I wasn't able to find any setting in the admin tools to set the correct localhost or 127.0.0.1 server...
what do you think about it?
Bye