Postgres 9.2.4 for Windows (Vista) Dell Vostro 400, re-installation failure

Hi Folks

Context

As a beginner, I recently had problems specifying check constraints on
tables in Navicat for Postgres since this software kept helpfully
responding with 'syntax error', although I could not see what underlying SQL
it was producing, so I decided to try learning pgadmin. On trying to get
access to my database using this tool, I now had Server groups, Servers and
localhost (only had myConnection, Database and Schema in Navicat), so I
double-clicked on localhost to provide a password. I had no idea what this
was, so decided to uninstall Postgres to try and re-set it. I have
subsequently remembered what this was, and was asked again for a new one on
re-install, which I provided. Think it was the same as what I originally
had.

The Problem

On re-installing Postgres, I have not been able to get it to work. During
re-installation I get an error message to say the program exited with an
error code, but otherwise appears to be okay. However, when I go into
pgadmin and enter my password to connect to the server (any password gives
the same response), I get a popup saying 'Server doesn't listen', could not
connect, connection refused etc'. The setup defaults to port 5432 during the
install process. I've checked postgresql.conf which has not been installed,
but I've looked at an old copy that I moved into the data folder, and that
looks at port 5432. Navicat also fails to connect.

Postgres was working okay before, so I don't think it's a problem with my
system or firewall, as I have not changed anything. After my initial
install, I edited the registry to point to the D: drive, as I prefer to have
my data stored on a separate partition, and this worked okay. The uninstall
leaves the data folder intact, and appears to leave the old service password
in case other services use it. Consequently it will not allow me access to
pg.log, even with administrator privileges, only by using pgadmin. The
Postgres install will not install with a data folder that is not empty, so I
had to re-name my data folder to data_old, and moved the contents back in
afterwards. The registry seems to be pointing to the right place to find my
data.

From the install log (as attached), I see Postgres complains that
loadmodules.vbs and adminpack did not install correctly. When I inspected
the adminpack directory it was empty, but I'm thinking that there could be
something else wrong. On my latest attempt to re-install, I don't seem to be
able to get anywhere with pgadmin, as when I try to connect I get a fatal
password authentication error now.

It appears these problems may have been known about for a while, but not
fixed, something to do with the install system waiting for something to get
into a loop, which it never enters in the first place. Not sure if this is
the same as my problem:
http://postgresql.1045698.n5.nabble.com/problem-with-PG-install-script-on-Wi
ndows-td3209407.html

The main difficulty seems to be trying to re-install Postgres. If you
already have created a database, the install program balks at having a data
folder that is not empty, causing me to use the above workaround to copy
back my data afterwards. Should be able to do this!

Thanks

Stephen