Need help to restore database

Hi all,
we are facing with a struggle problem with PostgreSql database
production.
A client system based on pgsql is down because the database raise an
error message like " no left space on device". We have deleted some log
files on this machine and after a system restart the db (and the system)
was up&running. After two days the database has crashed again. Looking
the postgres log there was an error on xlog file (I have inspected the
directory pg_xlog and no files I found it). I'll try to re-build the
xlog file with pg_resetxlog. The utilities has created a new xlog file,
the postmaster process run, but any command pg_dump, etc I try to
execute failed. The system respond that there are not database in the
system. Can anyone help us ?

Thanks in advance
Giancarlo