In order to hard reset a Motorola A840, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Motorola A840 device will be brought back to the default configuration of a brand new device.
1. Press-hold the Power button until the phone turns on.
2. Now enter Menu > Settings > Security.
4. Continue by selecting Erase/Reset > Reset Phone.
4. Lastly, select OK and Yes. Done.