might be a DNS problem if it suddenly stopped working.
Maybe the Mysql server has dns problems, and can't do a reverse lookup on you own IP for some reason.
If the permissions where something like
grant all on blah.* to user@your-host.com instead of
grant all on blah.* to user@your.ip.adr.ess it might be just that.
Ask you database admin to "tail" the logfiles.