F5 Key doesn't work without Fn

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Diagnostics;

namespace Capture
{
static class Program
{

const int yourF5Key = 1234; // Replace 1234 with the actual value of the button
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
_hookID = SetHook(_proc);
UnhookWindowsHookEx(_hookID);
}

/****************************************/
private const int WH_KEYBOARD_LL = 13;
//private const int WH_KEYBOARD_LL = 13;
private const int WM_KEYDOWN = 0x0100;
private const int VK_F1 = 0x70;
private static LowLevelKeyboardProc _proc = HookCallback;
private static IntPtr _hookID = IntPtr.Zero;

private static IntPtr SetHook(LowLevelKeyboardProc proc)
{
using (Process curProcess = Process.GetCurrentProcess())
using (ProcessModule curModule = curProcess.MainModule)
{
return SetWindowsHookEx(WH_KEYBOARD_LL, proc,
GetModuleHandle(curModule.ModuleName), 0);
}
}

private delegate IntPtr LowLevelKeyboardProc(
int nCode, IntPtr wParam, IntPtr lParam);

private static IntPtr HookCallback(
int nCode, IntPtr wParam, IntPtr lParam)
{

if (nCode >= 0)
{
Keys number = (Keys)Marshal.ReadInt32(lParam); // Stores the key pressed into the number variable
if (number == (Keys)yourF5key){ // Check for your "F5" button
SendKeys.Send("{F5}"); // Sends F5
}
}
return CallNextHookEx(IntPtr.Zero, nCode, wParam, lParam);

}

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr SetWindowsHookEx(int idHook,
LowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool UnhookWindowsHookEx(IntPtr hhk);

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode,
IntPtr wParam, IntPtr lParam);

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr GetModuleHandle(string lpModuleName);
}
}

Keys number = (Keys)Marshal.ReadInt32(lParam);

if (number == yourF5keynumber)

SendKeys.Send("{F5}");