If it was there when you turned it off (and the computer wasn't lingering in shutdown while you walked away), it should be there still (even if you can't see it).
In any case of potential data loss, DO NOT try to recover the data while using the same hard drive. You may be overwriting data in the process. You can consider booting a different computer with your hard drive connected to it, or running a Linux live disc, to get a look at the full contents of the drive. I've included an excerpt from another answer of mine below:
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...(I do recommend establishing a dual-boot Windows-Linux system), you can download a burn a live disc of Ubuntu Linux (http://distrowatch.com/table.php?distribution=ubuntu) or Parted Magic (http://distrowatch.com/table.php?distribution=partedmagic). A "live disc" offers a bootable and full-featured operating system (Linux, in this case) that runs from your optical drive and RAM. When you connect your external hard drive while at the Desktop of your live disc, you will hopefully have luck accessing and harvesting your data...
Ubuntu is more conventional in appearance and more straightforward than Parted Magic (a utility live disc), but the latter is also a smaller download and not difficult to understand.
When at the Desktop of Ubuntu, for example, your drives/partitions -- both internal and external -- should appear as disk drive icons on the Desktop. Treat them as folders, and transfer data between them as you wish.
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Remember, if you are trying to recover data from a drive, use a DIFFERENT drive to boot and access it, download programs, troubleshoot, etc. If Recuva doesn't find anything, you might try GetDataBack for NTFS file systems (www.runtime.org/gdb.htm); it's a limited, free trial version, but it's effective to verify that your data is still there.
Good luck. (Edit your question if you need more assistance.)