In windows 7,you can use BitLocker Drive Encryption to help protect all files stored on the drive Windows is installed on (operating system drive) and on fixed data drives (such as internal hard drives). Your can use BitLocker To Go to help protect all files stored on removable data drives (such as external hard drives or USB flash drives).
You can turn off BitLocker at any time, either temporarily by suspending it, or permanently by decrypting the drive.
To launch BitLocker Drive Encryption,just open Control Panel,then select BitLocker Drive Encryption.
To turn on BitLocker
Click Turn On BitLocker. This opens the BitLocker setup wizard. Follow the instructions in the wizard. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
To turn off or temporarily suspend BitLocker
To temporarily suspend BitLocker, click Suspend Protection, and then click Yes.
To turn off BitLocker and decrypt the drive, click Turn Off BitLocker, and then click Decrypt Drive.