The server is probably not down. If you can see any statistics at all, you know the server is up. However, it is possible that statistics have fallen behind.

There are frequently errors during stats processing. These need to be dealt with and repaired before the next stats batch can be run; thus, it is not unusual for stats to lag by about a week — particularly at the beginning of the week, when we may need to deal with errors that occurred over the weekend.

All told, do not be alarmed unless stats lag by more than a week.