Visual Studio. Code changes don't do anything

It sometimes happens that some files "are being used by another process".

Close your solution and delete all "bin" and "obj" subfolders of all your projects that are included in the solution.

Then open your solution again, execute "Clean solution" and build it again.

Check this setting in Tools/Options, then under Projects and Solutions>Build and Run.

On Run, when build or deployment errors occur:

My personal preference is for this value to be 'Do not launch'. It will prevent Visual Studio from launching the "last successful build".

Try Ctrl+Shift+B. This will build your solution (not just a particular project). Other environments might build when you save but this needs to be explicit in Visual Studio.