I've heard hard disk passwords are supposed to be secure. Unfortunately, these are still vulnerable to brute force attacks.
Yes, provided you have sufficient computing power, how much exactly depending on the strength of the encryption, you can brute force anything.
That's why we use session keys - a randomly generated key used to encrypt data. The session key is generated (and thus different) for each encryption. Session keys are typically symmetric keys - which means you use the same key to encrypt and decrypt. Encryption using symmetric algorithms are typically faster - thus encryption large amount of data won't be too much of a problem.
Then the session key is encrypted with asymmetric key - the public/private key pairs you usually hear about. The private key is held by the receiver, and is never revealed. The public key of the receiver is given to anyone who needs to send confidential data to the receiver. The public key will be used to encrypt the session key in the previous paragraph, and then the encrypted data plus the encrypted session key will be delivered to the receiver. The receiver then decrypt the encrypted session key with his private key, and then use the decrypted session key to decrypt the data. Asymmetric algorithms are typically much slower than symmetric ones - but this is less of a problem as it is only used to encrypt a relatively short session key.
Since the session key changes on each encryption, hackers will be spending a lot of effort to crack the encryption to gain just a single piece of data. On top of that, the public/private key pairs are periodically updated (with old data re-encrypted), giving less hints to hackers (with more and more data encrypted using the same key, cracking becomes easier) and making it even more futile to brute force.
And some systems will limit how many times you can present a wrong password... after that the data will be blocked or even self-destruct.
Though, of course, there are other ways to attack.