Postgresql Data directory Issue

Dear all,

I have a database server ( 10 databases near about 110 GB) running
Postgresql-.8.3 )
Today I need to format that system but I an facing the below issues :-

1. I am trying to use the previous data directory
(/opt/PostgresPlus/8.3/data) in new Postgresql-8.4 installation but it
results in below error while installing :-

Data Directory
[/media/a519e535-62a8-43a2-af93-2323690a3177/opt/PostgresPlus/8.3/data]:
Error: The existing data directory (catalog version: 200711281) is not
compatible with this server (catalog version: 200904091).
Press [Enter] to continue :

So i think I need to install Postgresql-8.3 to use that data.

2. I installed Postgresql-8.3 in new server and trying to use the data
directory but it faces the below error :-

Existing data directory is not empty and it cannot able to use it .

Please note that I am not able to take the complete databases backup
because the database server is down and restarts when we start backups.

Any help will be appreciated.

Thanks