Reinstalling Postgres 8.1 on Window problem

Hi,

I had been using postgres 8.1 for few months without problem. However, due
to my administrator request, I need to change my existing postgres account
to have a better account name and password.

I tried the following

1. Manually modification

a. Manual add a new account and password (complex password with $ and
number)
b. Uses sc config to change the user and password of postgres window
services
c. Changed all necessary folder permission on postgres database
installation folder.

Problem meet

1. When I net start postgres, it told me that postgres service unable
to start and the error message is the service did not report error

2. I could not found any logs and error on postgres folder, window
system logs or window application log

2. Reinallation of postgres

a. Did a batch install script to reinstall
b. In the batch file, I created the new user with complex password
c. Backup existing database and schema
d. Uninstall the existing postgres database, inclusive of the removal
of data folder
e. Reinstall postgres 8.1 by msi with msiexec
f. Installation succeed and able to restore data backup

Problem meet

1. When I tried to restart postgres with net stop postgres followed by
net start postgres, it report the same thing as above (postgres service
unable to start and the error message is the service did not report error)

2. No error and logs found too

I can uninstall the error-prone reinstallation and revert to the old user
and password (5 char username and password). The installation works for the
old username and password. It can be net start and net stop repeatedly.

What could I have gone wrong or what step have I missed? Is there any other
better solution for such change of user and password migration?

Regards,

Thompson