Sharepoint 3.0 was working fine. Yesterday night our server got updated with the update Microsoft WSS 3.0 (KB932091).
The OWSTimer stopped working, and we could't open some files on document libraries. On the log files there where a message saying that the update process was updating, but it was updating for a loooong time…
We had to remove the access to the database configuration (dns key) on registry, uninstall Sharepoint and install it again.
Thanks to João Mendes for this information.