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When you delete a file, Windows only marks the file as deleted, but doesn't actually remove it from your system. Those files are only truly deleted (well, replaced actually) when other data is saved to the same location on your hard drive.
There are some good software tools out there that will scan your system for deleted files. In many cases they can recover deleted files, even if they've been moved to the Recycle Bin or if the drive has been formatted.
File Recover from PC Tools is one such program that can find files that were deleted and will allow you to recover them.
I was able to recover a year's worth of photos that I accidentally deleted from my wife's laptop, even after reinstalling Windows using the restore CD that came with her computer.
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