All the company details have disappeared.
This is a known problem and Sage is already informed of the issue. I have read reports on various forums and saw users who had the same issue as you: the companies disappeared. The problem has been encountered on installations where Windows version was 8.1.
I recommend checking for an update to the application. Go to Help > Check for updates or stay updated through the official website of the developer.
Official website: http://www.sagepastel.com/Sage-Pastel-Software-Products/Pastel-Xpress.asp