Lightroom 4.3 Problem - Hope you can help

I have been using Lightroom 4.1 satisfactorily, although slowly, on my computer for some time.

Deciding to update to version 4.3 I downloaded the "Lightroom_4_LS11_win_4_3.exe" (790,011 KB) from the Adobe Web Site. I cannot get it to load - the wheel symbol runs for a few seconds after I double click the file and then stops. I have tried "Run as Administrator" and "Open" from the right click option list - the same happens. I have downloaded the file 3 times and none of them will install Lightroom 4.3.

Has anyone had a problem getting the program to install?  Did you solve it and how ?

Any help would be appreciated.

My O/S is Windows Vista SP2 Home Premium Edition and the systems meets the minimum requirements, and exceeds it. And Lightroom 4.1 runs OK.

Shamley