PostgreSQL fails to start

I've installed postgreSQL 8.4 on a Windows XP machine, and I can't get
it to start. Choosing Start Server from the menu produces a DOS box
that remains blank for about 3 minutes, then comes up with this error
message:

The postgresql-8.4 service is starting.................................
The postgresql-8.4 service could not be started.
The service did not report an error.
More help is available by typing NET HELPMSG 3534.
The start command returned an error (2)
Press <return> to continue...

Typing the suggested command actually produces no help other than what
has already been printed.

I do normally use NOD32 anti-virus and Windows Firewall. I uninstalled
NOD32 before installing postgreSQL, and disabled the firewall. This was
the state of the machine when the above error message was produced. I
get the same error if NOD32 and the firewall are running.

As far as I can tell, no log files have been produced. Therefore I am
at a loss as to how to proceed. Any ideas?

Eddie