In order to hard reset a Siemens C75, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Siemens C75 device will be brought back to the default configuration of a brand new device.
1. Power on the cell phone.
2. Now tap this secret code: *#9999#
3. Then your phone will restarts.