Hard Drive deleting files after I open them/some already missing

We have an external hard drive at work and when I came in after the new year break there was a bunch of files missing. I tried to open an excel spreadsheet then it came up with errors and wouldnt open, then when i went back to try and re-open it, it wasn't there, nor alot of other stuff. When i went into excel it was in the recently opened file, so i tried to open it from there and it wouldnt. I then clicked take me to the location of this excel document and it went to the correct file, but the spreadsheet wasnt there?

We're missing excel spreasheets and folders with word documents in them.

Please help!