Reinstalling PT4 will not help if PostgreSQL is not running. It sounds like you have PostgreSQL 9.0 working OK and if you have all your hand histories then you can import to a new database using that until we can check out whether your old 8.3 database can be recovered.
It's a sad fact of life that computer failures can cause file problems at any time, and you should always keep backups of your system, or at least any important files. PT4 has a
Backup mechanism built in, and we recommend all users to make regular backups so that you can recover in the case of a computer issue like this.
However, if you have all of your hand histories then you can at least re-import from those into a new database.
It may also still be possible to recover your old database, but that will have to be done via your ticket.