app in-order to set lock time dynamically for pc ?

Yes same thing i suggested . But according to security contraints system lock time cant be set more than 15 m hardcoded i.e so this app should be designed to oveeride system lock time with our time .. only wen we run the app ..

I guess this thing is achieved using some other scripting lang someone said me ..

So can i say C# libraries have no such strength to achieve this task but other things may do it .

Well, it sounds to me like your testers are running up against the system setting for minutes of idle time before the computer is put automatically to sleep, which has been set to too low a value.

The code given above won't lengthen that time but it may shorten it, so it's not what you want.

Rather than trying to do anything programatically, I'd have thought it would be better if individual testers could change the setting on their machine to a value they're happy with.

On Windows 7, it can be set from Control Panel -> All Control Panel Options -> Power Options -> Change Plan Settings. In the case of a laptop there are two settings depending on whether the machine is running on battery or mains power.

Actually its a real time senario for testers while they run SOME code testing via tool if system is idle with no mouse movement or whatever system goes into lock mode just because of that the tool which is under testing is getting effected itseems ..

This application just need to avoid that , so tester can keep the system idle and run this created application with setting time only to specify how many minutes after the lock should be applied till then LOCK should not be applied ..

I hope i am clear . any clarity i will try to help up :) 

Anyways the code given by you looks complex enough to understand but will try to crack at it .

and you said 

// rest of form code

it means like a message like thing or can i design a count down timer specifying HOW many minutes to lock ?? ?? I hope this looks cool right ? and also cancel option to abort the process ..

Ty so so much 

If you're wanting to add this functionality to, say, any windows form application, then you could go about it as follows.

You'll need to add a reference to your project to Microsoft.VisualBasic.dll as we're going to use VB.NET's InputBox function.

First of all make the highlighted changes to program.cs:

using VBI = Microsoft.VisualBasic.Interaction;

// ...

    static class Program
    {
        internal static int MinsBeforeLock;
        ///

        /// The main entry point for the application.
        ///

        [STAThread]
        static void Main()
        {          
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            string prompt = "How many minutes before screen is locked?";
            string title = "Set Time Before Screen Locked";
            string defResponse = "60";
            object result = VBI.InputBox(prompt, title, defResponse);
            int.TryParse(result.ToString(), out MinsBeforeLock);
            Application.Run(new Form1());
        }
    }

Now, add a Timer to your main form (Form1 say), double click on it to create a Tick event handler, double click on the Form to create a Load event handler and add the following code:

using System.Runtime.InteropServices;

// ...

    public partial class Form1 : Form
    {
        [DllImport("user32.dll", SetLastError = true)]
        static extern bool LockWorkStation();

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            int mins = Program.MinsBeforeLock;
            if (mins < 1)
            {
                MessageBox.Show( "Invalid response. Default delay of 60 minutes is being used", "Set Time To Lock Screen - ERROR!");
                mins = 60;
            }
            timer1.Interval = mins * 60 * 1000;
            timer1.Start();
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            timer1.Stop();
            bool isLocked = LockWorkStation();

            if (!isLocked)
            {
                throw new Win32Exception(Marshal.GetLastWin32Error());
            }
        }

        // rest of form code
    }

Now, as the code stands, the screen will only be locked if the application is still running at the appointed time. If the user closes it before then, the screen will not be locked.

Not sure whether this is exactly what you want but it's a start :)