The following bug has been logged online:

Bug reference: 1973
Logged by: Andri gunawan
Email address: cr34n (AT) hotpop (DOT) com
PostgreSQL version: 8.0.4
Operating system: WindowsXP Pro SP2
Description: Error on installation after uninstall PostgreSQL
Details:

Failde to conect to database. Procedural languages files are installed, but
are not activated in any databases.
server closed the connection unexpectedly. This probably means the server
terminated abnormally before or while processing the request.
Failed to connect to database. Contrib files are instlled, but are not
activated in any databases.

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TIP 2: Don't 'kill -9' the postmaster