Last Friday I tried to create a new sandbox in Enterprise Edition. It was in the queue all day, so I went home figuring it would be ready by Monday morning. I came in today and now the Sandboxes option is missing altogether. We are in Enterprise Edition, and I have Modify All Data and View Setup Configuration enabled on my profile. Does anybody have any ideas as to why this happened?
The only thoughts I have on this are three fold:
1) Are you accidentally actually logged into the Sandbox? When you are you won't have this option in Setup (I always accidentally end up trying to access Sandbox setup from a Sandbox)
2) Are you definitely in a full (not trial period) Enterprise Edition of Salesforce? Not in a Developer Edition (which do come at enterprise level) or a trial from your AE - which I don't think have Sandboxes.
3) Do you definitely have a sandbox? It seems unlikely that you wouldn't have one if you have purchased enterprise licences, it might be worth contacting your Salesforce AE (your company sales person might have to do this) to be sure you are properly licenced.