postgreslog - panic message

hi,
i am getting the following error messages:

<2006-05-24 15:28:08 CDT%>LOG: could not bind IPv4 socket: Address already in use
<2006-05-24 15:28:08 CDT%>HINT: Is another postmaster already running on port 5432? If not, wait a few seconds and retry.
<2006-05-24 15:28:08 CDT%>WARNING: could not create listen socket for "localhost"
<2006-05-24 15:28:08 CDT%>LOG: database system was shut down at 2006-05-24 15:28:08 CDT

<2006-05-24 16:19:39 CDT%>PANIC: could not locate a valid checkpoint record
<2006-05-24 16:19:39 CDT%>LOG: startup process (PID 6548) was terminated by signal 6
<2006-05-24 16:19:39 CDT%>LOG: aborting startup due to startup process failure
<2006-05-24 16:21:28 CDT%>LOG: database system was shut down at 2006-05-24 16:01:00 CDT
<2006-05-24 16:21:28 CDT%>LOG: record with zero length at 0/AC92BC
<2006-05-24 16:21:28 CDT%>LOG: invalid primary checkpoint record
<2006-05-24 16:21:28 CDT%>LOG: record with zero length at 0/AC9280
<2006-05-24 16:21:28 CDT%>LOG: invalid secondary checkpoint record
<2006-05-24 16:21:28 CDT%>PANIC: could not locate a valid checkpoint record
<2006-05-24 16:21:28 CDT%>LOG: startup process (PID 8428) was terminated by signal 6

i am using postgres 8.0.0

please tell as to what might be going wrong.
thanks,
regards
Surabhi