You're in the wrong forum for that particular issue! Having said that:
It depends on what's caused the data to disappear. If the disk has been quick-formatted, you should be able to get some data back. If the disk has been fully overwritten, that's going to be a problem...
When dealing with lost data you generally have two options:
1) Contact a data recovery company
2) Attempt to recover the data yourself
If you're going to do it yourself, you are advised to clone the hard disk first so you have something to fall back on if recovery doesn't work - either use a Linux Live CD and use dd, or find a package for your current system (Windows?) that will do it.
For recovering data, there are many packages available. I've not got any experience with Windows packages, but I've had very good luck using TestDisk [http://www.cgsecurity.org/wiki/TestDisk] under Linux.
Can anyone else suggest some appropriate software that runs under Windows?
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