Some comments and a possible solution below.
On Friday 26th April my Win10 laptop was updated automatically. When the system re-started my NVDA voice had been replaced by Hazel. On investigation I had lost all voices except Hazel, listed under Microsoft API version 5 and George, listed under Windows one core voices. The voice I had lost was male,I probably have the same Windows update, but no such problem. I have access to David, Mark, and Zira (Zira not Zero) across the two MS APIs.
At the time I was running nvda Feb 19, so I updated to March 19. This madeJust something you may want to know: The NVDA versions are not Feb and March. The NVDA version number is a four digit number representing the year, like 2019 or 2020. Then it has a period, and a single digit number usually between 1 and 4. These do not represent months. It may also have another period, followed by a single digit number. These do not represent days.
In short, 2019.2.1 is not a date, but a version number with three parts, which some voices read as a date because they aren't smart enough to know not to.
That will not hurt you in this situation, but it may be useful to know in other situations. Also, NVDA is now up to 2020.1 (Which, again, is not January, but just means the first version released in year series 2020).
You may want to try upgrading to that.
2 What synthesizers and voices come as standard with nvda?Espeak, and all of its voices and variants. All the rest come standard with Windows, and NVDA just utilizes them.
3 Would an un-install and re-install fix my problem? I have not tried this as I would need sighted help.You wouldn't need sighted help. The solution there, is to use Narrator.
In windows, with NVDA shut down, press control+windows+enter, and Narrator will start.
You could get everything ready in NVDA (pre-open relevant windows, download files, etc.), then switch to Narrator for the minimum time necessary to remove NVDA and start the new installation.
That said, it seems very unlikely that you need to reinstall.
Most probably, Windows removed the voices for some reason. To try to get them back, press your windows key and type "speech".
Move down to "speech settings", and press enter.
Then tab over to the "Manage voices" group, and you should be on the "add voices" button.
Press enter on that, and you will be able to enter and choose your language, and then install the appropriate voice pack(s).
In this case, you'll want to install the English (US) voice pack.
Once you select and install the voice, close everything and restart NVDA.
That should solve your problem. If not, post back with exactly what you did and what happened, and someone will probably have further ideas.
5 How can I download the latest User Manual?The NVDA user manual is always available on the menu.
Press NVDA+n, h, u, and you will be looking at the user guide.
If you want the actual file, while your browser has that open, go to the address bar (for example with control+l), and from there you can copy the path to the actual manual file, which is on your system already.
On mine it is in c:\Program Files (x86)\NVDA\documentation\en\userGuide.html