I am not too sure what I have done to cause this, but even after undoing all my edits, this error still appears

Error 1 Cannot autodetect which importer to use for "Program.cs". There are no importers which handle this file type. Specify the importer that handles this file type in your project. (filepath)\Advanced Pong\AdvancedPongContent\Program.cs Advanced Pong

After receiving this error, everything between #if and #endif in the program.cs fades grey

using System;

namespace Advanced_Pong
{
#if WINDOWS || XBOX
static class Program
 {
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    static void Main(string[] args)
    {
        using (Game1 game = new Game1())
        {
            game.Run();
        }
    }
 }
#endif
}

I have searched this and could not find a solution anywhere. Any help is appreciated.