TrueCrypt is no longer a secure alternative for encryption. See Why TrueCrypt Is No Longer a Choice
In an age that loudly proclaims the death of privacy, there still some things one prefers to keep to oneself; and the contents of one's laptop are likely to be among them. Financial records, medical correspondence, and legal communications are among the potentially legitimate but sensitive information one might carry on one's laptop. And despite close attention and careful precautions, laptops sometimes get lost or stolen. Under these circumstances, an account password is not enough to keep data safe. Fortunately, however, full disk encryption is now easier to implement than ever.
One longtime popular implementation of disk encryption is TrueCrypt, which has the advantages of being a free, independent, third-party application whose source code is open to inspection. Opening the code to inspection helps insure that there are no "back doors," or means by which law enforcement, three-letter agencies, or hackers could more easily decrypt the drive without having to crack the code or guess the password. TrueCrypt remains a respected and viable means of encrypting a drive, but it is perhaps not the easiest way to do it on a Windows computer.
On Windows PC's running Windows 7 Ultimate or Enterprise or Windows 8 Pro or Enterprise, Microsoft has implemented full disk encryption software known as BitLocker. If you are using modern hardware, right-clicking on the (non-boot) drive you wish to encrypt and setting a password should be all that is necessary to encrypt the drive. Remember the password, because you henceforward need it to access your encrypted drive every time you boot the computer. (On some older machines, it may be necessary to disable the requirement for TPM in order to encrypt. See BitLocker FAQ.)