How to force my C# Winforms program run as administrator on any computer?

You can embed this manifest into your application.

<?xml version="1.0" encoding="utf-8" ?> 
<asmv1:assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1" xmlns:asmv1="urn:schemas-microsoft-com:asm.v1" xmlns:asmv2="urn:schemas-microsoft-com:asm.v2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <assemblyIdentity version="1.0.0.0" name="MyApplication" />
    <trustInfo xmlns="urn:schemas-microsoft-com:asm.v2">
        <security>
            <requestedPrivileges xmlns="urn:schemas-microsoft-com:asm.v3">
                <requestedExecutionLevel level="requireAdministrator" uiAccess="false" />
            </requestedPrivileges>
        </security>
    </trustInfo>
</asmv1:assembly>  

Here is the sample code to run your application as admin.

ProcessStartInfo proc = new ProcessStartInfo();
proc.UseShellExecute = true;
proc.WorkingDirectory = Environment.CurrentDirectory;
proc.FileName = Application.ExecutablePath;
proc.Verb = "runas";
try
{
    Process.Start(proc);
}
catch
{
    // The user refused the elevation.
    // Do nothing and return directly ...
    return;
}
Application.Exit();  // Quit itself

Set the ProcessStartInfo.Verb to “runas” will let it run as admin. Here is related FAQ

http://social.msdn.microsoft.com/Forums/en-US/winforms/thread/28f84724-af3e-4fa1-bd86-b0d1499eaefa#x_FAQAnswer91

The obvious answer is to add a manifest file to the C# project and add the following line:

<requestedExecutionLevel level="requireAdministrator" uiAccess="false" />

But, a rather unorthodox approach can also be taken. We know that registry access requires administrator privileges. So, if you have a function that contains a registry write access, the function will throw a System.Security.SecurityException if you don't run the program as an administrator. It is implied that you have to call this function at the beginning of the program. If this exception is thrown, you can inform the user to run the program as an administrator and close the program.

public void enforceAdminPrivilegesWorkaround()
{
    RegistryKey rk;
    string registryPath = @"SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\";

    try
    {
        if(Environment.Is64BitOperatingSystem)
        {
            rk = RegistryKey.OpenBaseKey(Microsoft.Win32.RegistryHive.LocalMachine, RegistryView.Registry64);
        }
        else
        {
            rk = RegistryKey.OpenBaseKey(Microsoft.Win32.RegistryHive.LocalMachine, RegistryView.Registry32);
        }

        rk = rk.OpenSubKey(registryPath, true);
    }
    catch(System.Security.SecurityException ex)
    {
        MessageBox.Show("Please run as administrator");
        System.Environment.Exit(1);
    }
    catch(Exception e)
    {
        MessageBox.Show(e.Message);
    }
}

Here, the true in line rk = rk.OpenSubKey(registryPath, true) tells the program that it needs write access to the registry.