In order to hard reset a Sony Ericsson W660, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Sony Ericsson W660 device will be brought back to the default configuration of a brand new device.
1. Switch on the phone.
2. Go to Menu > Settings > General > Master Reset.
3. Now select either Reset settings or Reset all. Select one of these and confirm. Voila, hard reset is complete.