Cura will not start slicing

[Browny 0]

I am a complete novice to 3D printing and need help to find where I am going wrong.Installed Cura 15.4.6 on a Windows machine.It starts and appears to be running ok.The printer settings were changed to what I think they should be.However when I load a stl file Cura will not slice the file.Could somebody please help me where I am going wrong and steer me in the right direction to fix the problem.

[savante21 0]

Does the slicing progress indicator change but show no progress?  Not sure about windows, but on a Mac, I had this issue that consistently occurred when connected to a an OpenVPN connection.  The log files showed that Cura was unable to connect to "Backend" 

[Browny 0]

I think the problem may be that my Windows machine is too old (Microsoft Vista Ultimate) and Cura is not compatible.Tried the program on my wife’s Apple Mac and it worked ok.Would prefer to use my old machine though.