In order to hard reset a Sony Ericsson V800, 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 V800 device will be brought back to the default configuration of a brand new device.
1. Turn on your PC and install Sony's PC Suite application, preferably from Sony's official website.
2. Turn on your phone.
3. Start the app and plug in your phone to your PC.
4. Open Tools and Phone repair. Find and select your phone's model.
5. Continue the instalation process that should now begin.
6. Allow the phone to reset and restart.
7. Done.