Problem with Sony MZ-N707

In addition to what the other folks say about usb transfers: There is a
possible hardware issue here as well

I have had this happen on a few occasions over the last decade.  Since
I'm using older (pre-NET) Md's, I am always using either LINE, Optical
or Mic inputs.  (A mixture depending on the job).

IN all cases the recorder showed normal record.... but the disk came out
and went back in blank.

Sometimes this was due to errors (mine) at the "Shutdown" point,,,
Example.  I dropped the recorder, just hard enough to trigger the "Open
door" switch, and re-set the disk, the TOC was never written to disk and
  thus, though the recording was there, I could not access it (This is
easily,... well not all that easily,,, fixed however)

In other cases I had a record-overwrite head failure.  Mini discs are
"Magneto optical" this means that a laser is used to heat up a tiny spot
equivalent to one bit to the point where a magnetic record head, just
like a cassette or DAT recorder's head, can "Flip" it one to zero or the
other way around.  Then a laser (at lower power) is used to read the
bits.  The magnetic head is called the "Record overwrite head" and rides
on top of the disc (lasers go down below)  In one case I found that I'd
jammed in a disk wrong, caught the edge of the (I'm going to say just
record here) record head and folded it back upon itself,,, Did not work
that way.  In another the lever that lowers the head had gotten out of
place, in yet another one of the support wires had broken... They are
also the "Working" wires (Carry current) so that did not work well, IN
two cases I was able to fix, in two I was not  I do not suggest
attempting self-repair unless it is a very old unit (one was an R-2) and
you feel you have "Nothing to loose" cause I could have turned that R-2
into an E-2 (play only) real easy messing with that head.

So, it is possible it's a hardware problem

So, the suggestion depends on the warranty status....

If it's under warranty... That's the suggestion