1. You need to be sure you are using a heatpump thermostat. Most heatpumps require the changeover solenoid (O on the subbase) to be energized for cooling. This is a fail-safe design, so that if the solenoid coil fails, you still have heat. Some others are backwards and utilize the 'B' subbase terminal to energize for cooling. Either way, you need to have a heatpump-specific thermostat. Most generic heat/cool stats will not work.
2. It certainly sounds like you lost the control circuit. With any luck there is a fuse for the control transformer or board. It will be located somewhere in the indoor unit (fancoil or furnace). If not, you're probably looking at replacing a transformer.
3. Though you have 5 wires, all 5 are not necessarily needed. You can wire a heatpump to operate with as little as 4 while some multistage, emergency heat unit need up to 10. BE SURE what you have in front of you before you start connecting wires.
4. To make matters worse, some manufacturers (Trane, for example) have used their own nomenclature for thermostat terminal indentification. Just when you think you've got it figured out you have to unlearn and start over.