Winapi suddenly causes problem to open game build

I am developing a MOBA like game and i want to make its client windowed and borderless (using external user32.dll). It worked fine until it suddenly stopped, with just one build i get window looking like this:

instead of: http://i.imgur.com/w4oNrZ6.jpg

Here's the code that should (and did for some time) do the work:

 using UnityEngine;
 using System;
 using System.Drawing;
 using System.Runtime.InteropServices;
 using UnityEngine.UI;
 
 public class WindowHandler : MonoBehaviour
 {
 
     private Rect ScreenPosition;
 
     [DllImport("user32.dll")]
     static extern IntPtr SetWindowLong(IntPtr hwnd, int _nIndex, int dwNewLong);
     [DllImport("user32.dll")]
     static extern bool SetWindowPos(IntPtr hWnd, int hWndInsertAfter, int X, int Y, int cx, int cy, uint uFlags);
     [DllImport("user32.dll")]
     static extern IntPtr GetForegroundWindow();
     [DllImport("user32.dll")]
     static extern bool GetCursorPos(out POINT mousePoint);
 
     [StructLayout(LayoutKind.Sequential)]
     public struct POINT
     {
         public int MouseX;
         public int MouseY;
 
         public static implicit operator Point(POINT point)
         {
             return new Point(point.MouseX, point.MouseY);
         }
     }
 
     const uint SWP_SHOWWINDOW = 0x0040;
     const int GWL_STYLE = -16;
     const int WS_BORDER = 1;
 
     private const int width = 1380;
     private const int height = 780;
 
     private Vector2 ClickPos;
     private Vector2 MousePos;
     private Vector2 WindowPos;
 
     public static Point GetCursorPosition()
     {
         POINT Point;
         GetCursorPos(out Point);
         return Point;
     }
 
     void Start()
     {
         ScreenPosition.width = width;
         ScreenPosition.height = height;
         ScreenPosition.x = 270;
         ScreenPosition.y = 150;
         SetWindowLong(GetForegroundWindow(), GWL_STYLE, WS_BORDER);
         bool result = SetWindowPos(GetForegroundWindow(), 0, (int)ScreenPosition.x, (int)ScreenPosition.y, (int)ScreenPosition.width, (int)ScreenPosition.height, SWP_SHOWWINDOW);
     }
 
     void Update()
     {
         Ray Ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         RaycastHit RaycastHit;
         if (Physics.Raycast(Ray, out RaycastHit))
         {
             if (RaycastHit.collider.name == "Window")
             {
                 if (Input.GetMouseButtonDown(0))
                 {
                     ClickPos.x = GetCursorPosition().X;
                     ClickPos.y = GetCursorPosition().Y;
                     //ScreenPosition.x = WindowPos.x;
                     //ScreenPosition.y = WindowPos.y;
                 }
                 if (Input.GetMouseButton(0))
                 {
 
                     MousePos.x = GetCursorPosition().X;
                     MousePos.y = GetCursorPosition().Y;
                     WindowPos.x = ScreenPosition.x + MousePos.x - ClickPos.x;
                     WindowPos.y = ScreenPosition.y + MousePos.y - ClickPos.y;
                     SetWindowPos(GetForegroundWindow(), 0, (int)WindowPos.x, (int)WindowPos.y, (int)ScreenPosition.width, (int)ScreenPosition.height, SWP_SHOWWINDOW);
                 }
             }
         }
     }
 }

It has to be problem with my PC, cause when i run this build on another PC it works fine, and i dont really have a clue how to fix it. Thanks in advance.