I was writing my PHd thesis and I had one month working on it on the same word file. Today while I was writting the last pagese my file where I was working was blocked due to the appearence of the colorful sppining circul. I couldnt writte so I restarted my mac. After its restart the phd file appeared again for a couple of min, the sppining circul appeared again as well and after 2-3 sec every eorf was concerted in number and my file was unreadable.