I want to simulate F5 key press in my c# program, When IE is open I want to be able refresh my website automatically.
The easiest way to send (simulate) KeyStrokes to any window is to use the SendKeys.Send method of .NET Framework.
Checkout this very intuitive MSDN article http://msdn.microsoft.com/en-us/library/system.windows.forms.sendkeys.aspx
Particularly for your case, if your browser window is in focus, sending F5 would just involve the following line of code:
SendKeys.Send("{F5}");