Hi! I am using Audacity 2.0.5 on Windows 10. I was recording an audio for my video and it was going fine at first, the waveform is visible. But when I tried to save it, it wouldn’t work. It an error saying perhaps it’s not writable or my disk might be full, so I freed up some space on disk C. But I realized it’s already flat line. I tried exporting the file to MP3 and WAV but it’s just a 2-hour silence. Is there any way for me to recover the recording? It’s really frustrating. 
I tried exporting the file to MP3 and WAV but it’s just a 2-hour silence.
By any chance, did you save the Audacity Project? If you saved an AUP file, did you move it?
You may be out-of luck.
[u]AUP Project files[/u] contain many small files and it’s easy to foul things up, especially if you move, copy, or share projects.
Usually, WAV files are “foolproof” but apparently something went wrong before you exported (or the file didn’t get exported successfully). I always recommend exporting to WAV immediately after recording, whether you save an Audacity Project or not. Then, you can make back-ups from there depending on how critical the recording is.
There is a 4GB file-size limit for WAV files, but 2 hours should be OK unless you are saving a “high resolution” file or a multi-channel file, etc. There is no “artificial limit” for MP3 files (or most other audio formats.
…Computers are the least reliable things we own (and there are lots of settings that can be messed-up, etc.). And, sometimes you don’t even know there was a problem until you try to play-back the next day. If you are recording something super critical where there’s not possibility or “take two”, I always recommend two recording systems in parallel.
There are things to make recording more reliable (pro studios are now using computers) and that mostly involves dedicating a computer to recording & audio and not messing with it otherwise. ('And of course, making backups.)
Solid state recorders tend to be more reliable but sometimes “stuff happens” with them too.
It an error saying perhaps it’s not writable or my disk might be full,
That’s also the error you can get if you used unsupported punctuation marks in your filename. Today is not 1/27/20. It’s 2020-01-27. No slash marks.
Upper case letters, lower case letters, numbers, -dash- and underscore. That’s the whole filename character list. I’m professionally obsessive, so I don’t use spaces, either.
Koz
In case that looks a little too obscene, that’s the production list for this picture.
That’s not trick photography. People have hamburgers here from all over the world for this experience.
Koz
Was that it? You put a date in your name and the machine got confused?
If it is, then you know how to fix it next time. If not, then there’s something else wrong.
When you’re producing original content, it’s a good idea to Export recordings as WAV (Microsoft) 16-bit. That’s your protection backup if anything bad happens.
If you do have to use it, use a copy of the WAV file, not the file itself.
Koz