Audacity don't let me edit

I install audacity 2.1 in windows 10
but if i edit something the track goes from being like that

We don’t make any Audacity “2.1” version. We make an old “2.1.0” version.

I suggest you uninstall that “2.1” version and obtain Audacity 2.1.2 from us:

Half way through the installation, put a checkmark (tick) in the box that says “Reset Preferences”. Then when you start Audacity, say yes to resetting Preferences.

This will probably solve your problem, which I am guessing is because you have not yet saved an Audacity project and a clean-up application has decided to delete your Audacity temporary files for you. In 2.1.2, the Audacity temporary folder has been moved to a location that clean-up applications will not look in.

If that is not the problem, then did you import a WAV file, choose the option to read it directly, then move, delete or rename the WAV file? That would also cause the waveform to become a flat line.