You're using an AMD/ATI graphics card on 64-bit Windows with the AMD Catalyst 15.7 driver, and Lightroom/Lightroom 6 crashes or freezes during launch or when you edit an image in the Develop module.
This issue can occur when using AMD Radeon HD 5xxx to 8xxx Series graphics cards running driver versions 14.501.1003, 14.502.1014, and 15.200.1062.1004.
Install the AMD Catalyst 15.8 Beta Driver for Windows (posted on August 31, 2015).
This is counter to our normal recommendation and FAQ, which encourages users to update to the latest driver.
AMD beta drivers are final driver versions that have met regular QA standards before release. If you have questions about installing drivers, contact AMD.