2000 Nissan Micra Ignition and central locking

When turning off ignition, the digital odometer and clock flashes rapidly. When turning the ignition to the first position it stops flashing. When turning the ignition to on the usual dashboard lights do not come on although the engine starts. When turning on the ignition the doors lock and then unlock. This occurred over two days. Now the battery is flat, no power at all. The car has been taken to the local garage, however as a single woman with no experience of cars, I would value any information as to what the fault might be. I am also wondering if the key is at fault as the electronic open and close button on longer seem to work. Thank you. I am recently widowed, live alone in a rural area and have limited income.