The following are the things I experienced in the past: 1. Firewall/Virus scanner on AOS and/or SQL Server and/or Hyper-V killing the network connection. 2. Windows updates partly installed on AOS/HYPER-V/SQL 3. Non responding DNS (SQL checks connection every 30000ms and will kill after that) 4. Faulting network cables. 5. Maintenance tasks by system administrators on DC and/or DNS making them unavailable. 6. SQL is allowed to use all memory of the server and this crashed the server. 7. SQL databases (incl Tempdb) may grow more than harddiscs can handle, crashing the server. Especially when one or more databases or database files are stored on the C drive. The list I follow to track down the problem: 1. Check the EventViewer on AOS/SQL/DNS/DC 2. Install all downloaded windows updates and disable automatic installation. 3. Disable/uninstall firewall virus scanner. 4. Check database growth (if SQL restart occurred) 5. Replace all cables with new ones. 6. Yell at system administrators that I'm doing their jobs ;) PS reindex will never kill you're connection, but it will bump your memory usage because when run offline the index is removed and table locks will occur.
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