Help - Urgent

Hi,
I am unable to restart the PostgreSQL. I am using redhat Linux 9
with postgresql 7.4.5. Unexpectedly due to ups problem my server was
shutdown once. After that i am unable to restart the server. How to
stop and start.
Present status is running. If i tried to start i am getting as

1) bash-2.05b$ pg_ctl start
pg_ctl: Another postmaster may be running. Trying to start postmaster anyway.
FATAL: database files are incompatible with server
DETAIL: The data directory was initialized by PostgreSQL version 7.3,
which is not compatible with this version 7.4.5.
pg_ctl: cannot start postmaster
Examine the log output.

2)bash-2.05b$ pg_ctl restart
/usr/local/pgsql/bin/pg_ctl: line 274: kill: (5637) - No such process
waiting for postmaster to shut
down................................................................
failed
pg_ctl: postmaster does not shut down

3) bash-2.05b$ pg_ctl stop
/usr/local/pgsql/bin/pg_ctl: line 274: kill: (5637) - No such process
waiting for postmaster to shut
down................................................................
failed
pg_ctl: postmaster does not shut down

Note: Before my server shutdown i can able to do lot of times start /
stop / restart.
But now i am unable to stop it. Please help me.

--
Warm Regards,

S.ElayaRaja
Mobile: (+91) 98450 59540
E-Mail: elayaraja.s@gmail.com
raja_nk@hotmail.com