Scrivener 2,9 crashed and I can't reopen it.

Very impressed by the many positive testimonials Scrivener has received on Youtube and elsewhere, I downloaded the trial version of Scrivener 2.9 (to use with OS X Yosemite 10.10.5) on Wednesday, February 12, 2018 (Taiwan time). I read through the tutorial (long version) to familiarize myself with Scrivener’s various functions and was even more impressed by its many features. To try it out, I opened a project file, set up a complete outline (headings, sub-headings, etc.) of my doctoral dissertation and began entering text. I found the software very easy to work with and was happy with the way things were going. However, ten days later (Feb. 22) the “Force Quit” function showed that the Scrivener application was “not responding,” so I closed it by force quitting. This occasionally happens with MS Word for Mac, which always reopens with recovered files, so I assumed this would also be the case with Scrivener. However, the Scrivener application failed to reopen when I clicked on the Scrivener icon on my dock. I went into Applications and clicked on the Scrivener project file I’d been working on, but it would not open either. A pop-up appeared with the message “The application ‘Scrivener 2’ is not open anymore.” Consequently, I lost several days’ work. I was ten days into the 30-day trial period and was planning on purchasing Scrivener. I’d still like to buy the product because it makes writing so much easier, but I’m afraid the same thing might happen again. Do you have any suggestions or ideas of what might have gone wrong? All my other software applications are operating normally and I haven’t been experiencing any hardware problems.

Has anyone else had the problem? Would installing High Sierra and downloading Scrivener 3.0 be better approach? Thanks!