Problem with Postmaster

Dear sir,

I have problems to run the Postgres postmaster, please find below the
command I have input and the output of the system.

User Input:
-----------------
$ ipc-daemon2 &

System Output:
-----------------
[1] 392

User Input: (attempted to start postmaster)
-----------------
$ /usr/bin/pg_ctl -D /usr/share/postgresql/data start

System Output:
-----------------
pg_ctl: Another postmaster may be running. Trying to start postmaster
anyway.
Found a pre-existing shared memory block (key 5432001, id 0) still in use.
If you're sure there are no old backends still running,
remove the shared memory block with ipcrm(1), or just
delete "/usr/share/postgresql/data/postmaster.pid".
pg_ctl: cannot start postmaster
Examine the log output.

User Input:
------------------
$ /usr/bin/pg_ctl -D /usr/share/postgresql/data stop

System Output:
-----------------
kill 1724: No such process
waiting for postmaster to shut
down.............................................
................... failed
pg_ctl: postmaster does not shut down

I run cygwin for PostgreSQL on Window XP. I would be most grateful if
you could show me the proper command that should be keyed in and advise
me on how to:

- delete "/usr/share/postgresql/data/postmaster.pid"
- eliminate similar situation in the future

In fact, the postgres did not function after I have wrongly chosen the
scrolling function on the menu option bar at the top. The system did
not response to any of the keystroke that I made. I understand that I
should shut down the postmaster before exiting postgres, but at that
moment, I could do nothing except rebooting the whole system, it was
when the postmaster went wrong.

As I am a Hong Kong part-time evening student taking a computing and
information system degree course with University of London, I am working
on the assignment for database management (that's why I use
PostgreSQL). Frankly, I didn't come from any technical background, so
always came across some technical problems but didn't get the clue on
what's going on. Anyway, I would appreciate it if you could get back to
me a.s.a.p. so that I could focus on the assignment.

Thanks in advance for your help. Looking forward to hearing from you soon.

Best Regards,
Ruby