I recently downloaded Lightroom 5.5 for Windows 7 and it seemed to install correctly, but when I completed my registration and serial number it does not launch the application. When I try to manually open the program again, it takes me to the beginning of the registration and serial number process. I tried downloading the 5.7 version and have had the same proplem.
Do you get any sort of error message when you commit the serial number?
Does your serial number begin with "1160"?