The dashes on the MKIII mean that the display, either the Weather Oracle Multi (large) or smaller Oracle, have stopped receiving the signal from your sensor assembly. Based on the fact that yours has the clock/date, you have the larger multi-display.
Some initial questions:
Age of system?
Did this problem just happen?
Here are a few things to check:
Are there any 'new' electronic devices placed close to the Rainwise receiver (small black box)? This would be since the problem has occurred. If so, try moving the new device away. Also check to make sure the Rainwise receiver is at least 2-3 feet away from the display. Too close and it can cause interference itself.
You can also try moving your display to a different (closer) location.
Battery level
Does your system include the IP-100, if so, login to your account and check your battery level. If it's below 6 volts you may need to replace the battery.
If you have no IP-100 you can check the battery through the display. To do so however, you will need a signal received. Otherwise you'll have to pull the battery and test it using a volt meter.
The diagnostic mode (Large multi-display) is seldom needed or used. It provides
information about sensor unit voltage, software versions,
communications and the ability to reset the display back to factory
defaults.
To enter the Diagnostics Mode press MIN followed by SELECT.
HUMIDITY - shows the software versions of the display and sensor
unit. The two digits on the left represent the display version
number and the two on the right is the station version.
TEMPERATURE - for checking the battery condition of the sensor
unit. The value toggles between the current, maximum and
minimum battery voltage during the last 24 hours.
TIME - for communication diagnostics. The number on the right
indicates the reception of good data packets. Bad data packets
are displayed on the left.
WIND SPEED - for communication diagnostics. The value increments
with every data byte received. The number wraps at 100.
The byte count as well as the packet counters can be reset by
pressing the wind speed button.
Press SELECT to exit back to normal operation.
If you need a battery, here are a few links that might help:
http://www.amazon.com/Werker-WKA6-5F-5Ah-Replacement-Battery/dp/B00C80PYOMhttps://www.batteriesplus.com/replacement/battery/werker/wka65fHope this helps.