I have been successfully runing a trial of Lightroom CC. It expired. I bought Lightroom 6. I uninstalled LRCC and installed LR6. I ran it and told it to load my catalogue. It strarted but crashed. I restarted the PC and tried again. Same result. I tried it with my LR5 catalogue. If upgraded the catalogue and then crashed. I uninatalled, restarted and reinstalled. I tried again. It still crashed. What can I do? I am running Windows 10 on a 4MB laptop. I am travelling in Europe so I cannot ring Adobe Australia for help.
Try turning off the graphics acceleration. Go to Preferences, click on the Performance tab, then uncheck the box that says use Graphics Processor. If you can't get that far (becuase LR keeps crashing), then follow the instructions here under the heading "Manually disable the graphics processor". Adobe Lightroom GPU Troubleshooting and FAQ