The leading cause of VNA failures is problems with the VNA Solid State Drive (SSD). These problems are usually preventable (see Preventing VNA SSD Problems), and in many cases, recoverable. The following could save you weeks of downtime and the cost of replacing your VNA SSD.
This document is now on the Keysight VNA Support Website: http://na.support.keysight.com/pna/hdrecovery.html.
If your VNA does experience a Solid State Drive problem, you will not be able to access this Help file, but you may be able to access the Internet from another computer.