In Windows 8.1 when I open "Start Tor Browser.exe" in Windows Explorer nothing happens. Firewall and Antivirus are disabled
I experienced the same issue... deleted and downloaded twice before I discovered the problem.
download the tor bundle
right-click the application file
At the bottom, click "Properties"
You will see a notice that says "This program seems to have come from another computer.." click the box to enable.
Now, double click the file, Tor install modal opens on screen.