 How to encrypt a computer's system disk or disk C with BitLocker If this computer has a TPM module, but it was not used or initialized before, you should initialize it in order to turn it on. Open Control Panel – BitLocker Drive Encryption. Select Turn On BitLocker next to Disk C. For the TPM to turn on, you should restart the computer. After pressing F1, Windows will boot and you will see a BitLocker Encryption window showing that the TPM module is enabled. If the computer doesn't have a TPM module, you can use the Group Policy Editor to be able to use BitLocker without TPM. Press Windows Plus R and enter GPID.msc.