I'm running MacOS 10.10.5, and had been running Parallels Desktop 12. One morning when I tried to start Parallels it refused to start up. No error message, no crash, it just ended without getting to the menu. I uninstalled Parallels and tried to reinstall it from the disk image file. The Install app *also* wouldn't complete, again no error message. I finally had to reinstall Parallels 10.4.0 to get anything working. I hadn't changed my machine configuration or updated the OS (as far as I can remember). What is going on, and why doesn't it at least give me an error message?