GNUPG: lost secret key when machine shutdown


Im fairly new to this so please bear with me

I recently installed GNUPG for windows on a number of machines. I tested the installation and everything was working fine. Overnight the machines were switched off and in the morning when the users logged back on we appeared to have lost the “secret key”. We get a decryption failure message saying “no secret key”. One machine was left on overnight and still works fine

Any ideas why this would happen?