Missing row after update

Hi there. I am new to Postgresql but very familiar with RDBMS. We are
running 8.4 on windows serer 2008 r2. I was updating a record through
pgAdmin and was being an a$$ and pressed the run button multiple times
and then the record just disappeared. Update query:

update jaas_login set password=md5(login_name || ':' || realm_name ||
':Password123'), has_logged_in = false, modified=now(),
failed_attempts=0 where login_name like 'CompanyAdmin(at)%';

I cannot find the record at all so tried to re-insert it and the query
just runs and runs and runs.

We thought we had backups of this DB but all we have are dump files
and I really really don't want to have to restore if I can avoid it. I
find it hard to believe that a db as advanced as postgresql will just
"lose" data and there has to be some explaination for where the record
is.

Any help would really save my butt. Thanks

Dinsdale