Desktop alerts stopped working

Desktop alerts are no longer working for us. We run them on Chrome. For a while, no matter what browser (for example Firefox or IE), we were in, as long as Chrome was open and logged into our account, the desktop notifications would appear when we got a new chat. Now, even if Chrome is on top or the only one open, if we are in another tab other then the one logged into chat, the notifications don't appear. What might be going on? We are all running Windows 7. Is the problem perhaps that multiple (usually 5) people are logged into the account at a time (as we all monitor the chats)? Thank you kindly for any help you can provide.