Typically hard drive death comes in the form of mechanical failure, also called crashing. You will know your hard drive has crashed if your computer won't start up, and you can hear a quiet yet audible clicking sound coming from inside the PC tower. You also might get error messages like, "missing boot device", or "primary hard drive not found". This kind of hard drive failure can't be fixed, and all data on the drives can't be recovered, although there is a slim chance the old hard drive in the freezer trick might work, assuming you're willing to open up your PC and remove parts.
Besides hard drive failure, another common causes for data loss on PCs is virus infection. Most viruses only attack Windows system files and not your user data but sometimes viruses can corrupt your files turning their contents into gibberish, or they corrupt the Windows file system destroying your files and rendering your PC unable to boot. For more on virus infection you can read my post on that topic.
A good backup strategy will protect you from loosing your data in both of these scenarios. Copying your files to a CD-R might seem like a good idea, but they are too unreliable for safe-keeping. Even so-called archive quality CDRs should not be trusted.
A much better backup solution is to keep your important files on two separate hard drives at all times. If one hard drive fails or it's data becomes corrupted you repair or replace the bad drive, then copy your files from the other drive to the replaced or fixed drive. For example, if you own a desktop PC and a laptop you can copy all the important data from one to the other. If you only have one computer you can purchase an external hard drive and connect it to your PC via the USB port to copy your data to it.
The above backup methods will protect your data from the most common causes of loss but may not help in the event of fire, flood, earthquake or other disasters since both backups are in the same place. To protect your data from such disasters, you can back up your files to the Internet. There are free and paid online file backup services to choose from. The advantages of online file storage are you don't need to purchase any new hardware, and you can access your backed-up data anywhere you have internet access. Drawbacks are limited space on free accounts, and slower uploading and downloading speed compared to local backups.
Dropbox: is one option for online backups. It is very simple to set up and use. Once installed, it creates a folder on your PC that you can drag and drop files into. All files in the Dropbox folder automatically get backed up online, and you can also install it on all your PCs to keep files synchronized between PCs as well as on the web. Dropbox also has a web interface so you can access your Dropbox files from any PC with an Internet connection, without the need to install software. You just got to the Dropbox website and log in to access your files. The free account is limited to 2 gigabytes, paid options offer much more file storage space.
For more information about online file storage services, including a comparison chart of features of popular sites visit:
Wikipedia: A comparison of notable file hosting services
Cobian Backup: is a free backup program for Windows. You can use it to automatically run scheduled backups of files and folders from one hard drive on your computer to another, to a USB-connected external hard drive, to a computer over a local network, or to a server computer over the Internet. You can create full or incremental backups. Incremental backups allow you to save only changes to files since the last backup, thus minimizing hard disk use and backup time. This also allows you to save multiple versions of file changes for retrieval later if needed.
This is important because let's say you made changes to a document on Monday, then the automatic backup routine propagates those changes to the backup Monday night, replacing the previous night's backups. When you come in on Tuesday and realize you need to go back to Monday's version of the file, you can't because Tuesday's backups overwrote Mondays. Saving multiple past versions of the file changes solves this problem, and since only file changes are saved, multiple past versions of files don't take up a huge amount of hard drive space.
DirSyncPro: is a free, open source Windows backup program that is simple to set up and use. Like Cobian, it can create incremental backups to minimize disk space, but unlike Cobian it does not as of yet support backing up files over the Internet.