Data Recovery - All You Need To Know

Rescue disks are virtual copies of the operating system that you are running. Earlier, floppy disks were used, but with the advent of more complex OS, now CDs, and even DVDs are used.
Since your system cannot be used in most cases when you are trying to recover data, it is best to use a Rescue Disk instead.
Before all else though, you should consider using the best data recovery software available today:
Restore My Files

When you delete something, it is not automatically "deleted". Instead, it is labeled "over-write" by your computer and hidden from your view. Then, when you add new content, it over-writes the stuff that you deleted. This happens in the reverse order - the data that was deleted last, is over-written first.

So if you just discovered that you deleted a file, stop using the computer right away, as you might overwrite it.

There is some data recovery software, like Restore My Files (link above) that can restore this data. However, in some cases, professional help is needed, and this can cost in hundreds, and even thousands of dollars. This is especially true in the case of physical damage to the hard-disk.

One of the biggest mistakes that many people make is forgetting that there are cheaper options like software for data recovery available. Before you try anything else, make sure that you use the software first:
Restore My Files

If the software option doesn't help you, then you may need to enlist the help of a professional data recovery company, and evaluate whether the data you're trying to get back is valuable enough to spend hundreds of dollars on data recovery.