Data can exist in corrupted form (i.e., good data which is being stored incorrectly) and this is referred to as corrupt data. It may appear as the dissertation that opens as symbols, the QuickBooks file the program won’t open, or your wedding video that plays for just four seconds before dying. The repair needed to restore access to corrupted data depends on where the corruption resides: within the file(s), the file systems, or within the hard disk(s).
Drive level: damaged areas provide corrupted data (hardware failure symptoms); the goal for this step would be to image the drive prior to ‘a few strange files’ becoming ‘drive will not mount’. File system level: the file system’s directory listing has become disordered (files have disappeared; folder entries are garbage); the drive demands formatting and the data remains on the disk waiting to be restored. File level: the file was affected by the interruption (interrupted save/write; crashed during write), and recovery is about repairing structure to an item (i.e., rebuild headers; salvage streams; extract text & objects from Office documents; remux video when its index was never recorded). The diagnostic identifies the correct layer at which to begin treatment, because addressing the incorrect layer would waste time and put the data at risk.
Repair is simple in one way: it rebuilds your files’ structures. It doesn’t create the missing pieces of information. If you have a .docx file that has a broken wrapper but still contains all the original text, then repair will restore the entire document to how it was originally. Similarly if you had a video file that no longer contained an index which allowed it to play properly (i.e. a broken mpeg file) then repair will rebuild the proper index for you and allow the video to re-multiplex and run again. Even if your Excel file was damaged by corruption so badly that Excel will not open it, repair may still allow you to view the data within. However, if your computer crashed right after you clicked Save on your document, before the save finished, then there’s nothing to repair as the item didn’t exist. And, similarly, if you have a file where the middle third is filled with zeros (or garbage), then repair won’t magically fill in the holes. At the diagnostic, you’ll know whether each of your files is going to be rebuilt, recovered (extracted) or gone, free and before any decision.
Most often no. A full screen of symbols usually means there is damage to the “wrapper” around the contents of the document, but that the actual contents have been preserved enough to pull out the information, even if Word will not allow you to open the file. Please forward both your corrupted file as well as any temporary and/or backup versions with it: Microsoft Office tends to scatter pieces of the data throughout all versions of the file, and the recovery program can use them to “reconstruct” the document.
Yes, classically. This would be an error resulting from a corrupted or incomplete index (a fairly standard occurrence on video recordings where they were cut off); therefore, a re-mux operation would essentially create a new wrapper around footage that is completely intact. If the camera or card it came from is available, send that too, as the original source sometimes yields a cleaner copy.
On such a large scale, corruption is a sign of something going wrong, and therefore is no accident: failing disk, file system falling apart, or malware. Do not use this computer (and especially do not run repair programs on it), and bring us the hard drive. Trying to fix files one at a time while the problem continues is like trying to bail water from a sinking boat with the hole in the bottom unplugged.