If you are showing a caution sign on your Outlook, it normally means that you are not authenticating with the exchange server and have lost connection. You will need to do a couple of things;
1. Check to make sure that you have a network connection.
2. If so, then you need to check your settings to ensure that the authentication setup has not cleared itself.
3. Lastly, if all else fails, check to make sure that your account is not disabled.