could not locate a valid checkpoint record

Hi all,

We had a crash with our postgresql 7.4.5 and when we rebooted we have
this message :

 [1-1] LOG:  could not create IPv6 socket: Address family not supported
by protocol
 [2-1] LOG:  database system shutdown was interrupted at 2005-09-08
21:03:00 BST
[3-1] LOG:  could not open file
"/var/lib/pgsql/data/pg_xlog/0000000000000000" (log file 0, segment 0):
No such file or directory
[4-1] LOG:  invalid primary checkpoint record
[5-1] LOG:  could not open file
"/var/lib/pgsql/data/pg_xlog/0000000000000000" (log file 0, segment 0):
No such file or directory
 [6-1] LOG:  invalid secondary checkpoint record
[7-1] PANIC:  could not locate a valid checkpoint record
[2-1] LOG:  startup process (PID 24513) was terminated by signal 6
[3-1] LOG:  aborting startup due to startup process failure
 postgresql: Starting postgresql service:  failed

I tried ( after copying thes PGDATA dir obviously ) :

pg_resetxlog /var/lib/pgsql/data/ -f

After that postgreSQL starts but I realised that pg_database is empty (
it contains only template0 and template1 ) .
If I type "psql myDB", with myDB being a database present before the
crash, I have access to the psql shell but a "SELECT * from myDBtable"
gives me the right table column name but empty !!

myDB=# select * from myDBtable;
 id | use | data
----+-----+------
(0 rows)

How can I get the data back? I still have all the PGDATA/base directory.