Visual Studio doesn't open my c# solution

Dear all,

For some reasons i had to work from a different PC and I put all my project folder on a HD and then on the new PC. When I launch the Unity project, everything is working, but...

...if I double-click on a C# Script, it opens in Visual Studio 2019... but alone, like it wasn't part of a solution. Thus, I have anything in the 'Solution explorer' ans my classes aren't recognized by Visual Studio. However, if I open directly the file "mySolution.sln", it works : I have all my classes in the Solution explorer.

I tried to delete the sln file and reload the project, hopping that Unity would rebuild the solution, but it didn't change anything...

What should I do ???

 

No idea ?