I have Windows 2007 machine on which I have tried to install Postgres 8.3. At the end of the installation it pops a warning saying Error reading file C:/Program Files (x86) /PostgreSQL/8.3/data/postgresql.conf I checked for the file postgresql.conf in C:/Program Files (x86) /PostgreSQL/8.3 and found that it does not exist.
PostgreSQL 8.3 is no longer in support. Please try installing a supported version of PostgreSQL (at least 9.3 but preferably 10) and see if you are having the same issues there.