IMPORTANT ANNOUNCEMENTS AND HOT TOPICS:
GOG Galaxy - troubleshooting and useful informationThe Witcher 3: Wild Hunt - buying as a gift temporarily unavailable (fix in progress)The Witcher 3: Wild Hunt - downloading, redeeming and installing FAQThe Witcher 3: Wild Hunt - Nvidia code FAQ
Windows Vista uses functionality called UAC (User Account Control) which, among other things, scans executable files before launching them. This may cause the installer to be launched after a long delay, depending on its size (sometimes many minutes). You can bypass or disable UAC for the duration of the installation process to bypass this delay.
It is generally advisable to disable UAC altogether, as it is known to cause problems in some software, especially games, both old and new.
To disable UAC, please consult this support article.
You could also try launching the installer by right-clicking the setup file and selecting "Run as Administrator".
Finally, if your installer is divided into multiple files, make sure that you're trying to open the executable file (with an .exe extension and an orange icon) rather than a .bin file. The .bin files aren't disc image files, but archives used by the executable file.