Server stops responding in every week

PostgreSQL 9.0.1, compiled by Visual C++ build 1500, 64-bit
is installed in Windows 2008 server and servers 23 users in LAN 10 hours per
work day.

Approx once per week server stops responding: Users are waiting 4 minutes
for query to complete but nothing happens.

If postgres service is re-started in Windows Control panel, it continues
working for a week and same issue appears again.
Server and windows event log does not contian any information about issue.


How to fix of diagnose it ?
Should I move to 32 Postgres 9.0 server or other idea ?

Andrus.