The server down
Many times we do not know if there is a problem with the structure that houses our service has the server down.
Even the great weep
Are known examples from Facebook and Skype a few days ago.
Anyway there are community where all users report the status of the main server.
The best known are isitdownrightnow.com that in addition to collecting the reports run test nagios style.
A few days ago, for example, the 10/9/2015, at approximately 21: https://downdetector.com/status/google-drive/news/1620-problems-at-google-drive, the contents of our file on google drive were inaccessible for about an hour.