If you have an SD card or USB drive (or any storage media even your main hard disk!), you can recover the files (if the data is still there!) using PhotoRec_Win.exe and any Windows computer. PhotoRec_Win will try to recover all types of files, mp3, mp4, doc, etc., not just photos.
There are graphical Windows GUI utilities which are easier to use, but they tend not to be free or as good as this one.
If you want to try another Windows recovery tool, then I suggest the free (to try) version of Recuva (it costs £20 now if you want to actually recover any files but it is very useful in finding slightly older versions of files on your disk if your current version has become corrupt). Recuva has a nice Windows GUI interface and is easy to use. If this does not manage to recover all of your files (or you are too mean to fork out £20!) however, then PhotoRec is the way to go!
P.S. A friend of mine was working on a large Serif PagePlus PDF when he had a power cut. The file was corrupted and it contained a whole months work, but Recuva managed to find a slightly earlier version and recovered it. My friend said it was the best £20 he had ever spent!
I have personally used TestDisk to repair/recover corrupt flash media files in real situations three times now - again it performed very well and most of the files were recovered.
TestDisk runs under Windows 7 64-bit as well as other versions of Windows. TestDisk.exe is also included in the download which is useful if you need to restore/repair the drive or media, but I would always advise using PhotoRec_Win first.
Instructions are included with this utility, but here is my quick guide (tip: you will find it easier when downloading the utility if you use the Chrome Browser which will offer to translate the web pages).
PhotoRec documentation can be found online: - http://www.cgsecurity.org/wiki/PhotoRec
TestDisk documentation can be found online: - http://www.cgsecurity.org/wiki/TestDisk
If your hard disk has disk read errors, you may find the process stops or is very very slow - if so try using HDD Regenerator first (see Tutorial #64).
PhotRec/TestDisk may not know the name of the original file, so if you wish to recover a file which contains text (such as a .cmd, .txt, .bat, Excel, Word or other type of document file), use a search utility such as NirSoft SearchMyFiles. Set the search folder to that used by PhotRec to save the files and set the Text field to some text that you know is within your file. Once you have found a file that contains the text, you can make a copy of it and rename the file extension to the original type (e.g. .xls or .docx) and then try to open it by double-clicking it and see if it works (e.g. .docx should open in MS Word). If the file is encrypted (e.g. password protected Excel file) a text search will not work however. In this case, look at the length of each file recovered by PhotoRec to find one of approximately the correct size (you can use SearchMyFiles to find all files of a certain size range) - then rename it to the correct file extension (e.g. .xlsx) and see if you can open it. The file date of the recovered file cannot be relied upon, so there may be more than one version of the same file, so you may need to open and examine each one to find the latest version.