Postgresql – Error: Could not read Block X of relation base/Y/Z

We have some serious issues with our PostgreSQL-Server (Version 8.4). Our webapplication uses jdbc to connect to the PostgreSQL Server. Suddenly our webapplication cant connect to the PostgreSQL Server. We get the PSQLException: Broken Pipe. Cause of this, i tried to connect via pg_admin. This works, but i'm getting errors like this:

ERROR: could not read block 32570 of relation base/16390/2663: read
only 0 of 8192 bytes

I tried to make a dump to backup the data and this doesnt work too:
(Look on the edit at the bottom of the side)

pg_dump: SQL command failed

pg_dump: Error message from server: ERROR: could not read block 32570 of relation
base/16390/2663: read only 0 of
8192 bytes

pg_dump: The command was: LOCK TABLE
public.results_233_top100_disease_state_karyotype IN ACCESS SHARE MODE

I tried to get some information with

SELECT oid, relname FROM pg_class WHERE oid=2663

The result was this:

2663 ; "pg_class_relname_nsp_index"

During my effort of collecting some information, i read, that recreating that specific index could help. So reindexed it with the following command:

REINDEX INDEX pg_class_relname_nsp_index

This didnt helped at all, and now i'm pretty helpless. Has somebody an idea what i can do ? Another point is, that we do weekly backups. Is it possible to overwrite the data folder: /var/lib/postgresql/8.4./main with our data from the backup?

EDIT: I fixed the problem with reindexing the table that had the error. Now i'm getting another error:

pg_dump: SQL command failed
pg_dump: Error message from server: ERROR: invalid page header in block 1047 of relation base/16390/16398
pg_dump: The command was: COPY public.data_1 (sampleid, feature, value) TO stdout;