In order to hard reset a Sony Ericsson T105, 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 T105 device will be brought back to the default configuration of a brand new device.
1. First, install PC Suite.
2. Go to Tools and Phone repair.
3. Continue with the installation process. Done.