Open the extracted folder and look for Setup.exe or Install.exe .
Right-click on Part 1 and select "Extract Here" (using WinRAR or 7-Zip). The software will automatically pull data from the other three parts to form a single folder. Open the extracted folder and look for Setup
Always right-click the game shortcut and select Run as Administrator to avoid save-game or permission issues. Open the extracted folder and look for Setup