[dba-SQLServer] SQL Server timeouts

I am running this process that updates SQL Server from VB.Net.  The 
process runs normally for tens of millions of records, then SQL Server 
"hangs" and stops servicing requests (from this process), either reads 
or writes.  It just times out with error messages "Timeout Expired: The 
timeout period expired prior to completion of the operation or SQL 
Server is not responding".

This is not a once off occurrence, it happens every time I start the 
process running.  Sometimes I get this and then eventually SQL Server 
will start responding, sometimes it just stops responding.

How do I troubleshoot this?
-- 
John W. Colby
www.ColbyConsulting.com