ALL the messages disappeared from my Inbox

This is the second time in three months that ALL of the messages in my Inbox disappeared.  Deleted messages are still there, but the Inbox -- NOTHING.  Even my flagged messages are gone.  The last time I asked for help, I received a link that didn't work, from an e-mail that didn't take replies.   I tried calling for help, but the tech was more interested in selling me an anti-virus program than finding my lost mail.  He claimed the problem was a virus in my Dell computer.  The only problem with that explanation is that I was using a MacBook when I lost the mail.  How can I retrieve the lost messages and keep this from happening again?