Directive Needed:
using Microsoft.Win32;

Code:
RegistryKey rkApp = Registry.CurrentUser.OpenSubKey("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Run", true);

Add:
rkApp.SetValue("GamExe", Application.ExecutablePath.ToString());

Delete:
rkApp.DeleteValue("GamExe", false);

Check if Exists:
if (rkApp.GetValue("GamExe") == null)
{
chkRunWithWin.Checked = false;
}
else
{
chkRunWithWin.Checked = true;
}