Disable and enable buttons in C#

I am working on something fairly simple, well I thought it would be. What I want is when button1 is clicked I want it to disable button1 and enable button2. I get the error below: Error 1 Only assignment, call, increment, decrement, and new object expressions can be used as a statement.

private readonly Process proc = new Process();
    public Form1()
    {
        InitializeComponent();
        button2.Enabled = false;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        proc.StartInfo = new ProcessStartInfo {
            FileName = Environment.GetFolderPath(Environment.SpecialFolder.Windows) + "/explorer.exe",
            Arguments = @"D:\",
            UseShellExecute = false
        };
        proc.Start();
        button1.Enabled = false;
        button2.Enabled = true;
    }


    private void button2_Click(object sender, EventArgs e)
    {
        proc.Kill();
        button1.Enabled = true;
        button2.Enabled = false;
    }