Answer to "I only get a white screen with a crossed circle at startup"Problem Solved. First, turned your troubled Mac into an external hard drive by pressing the “T” key while starting up. Connect your troubled Mac to a good working Mac with the same OS or higher (connecting cables will vary depending on the year and model of your troubled Mac). Open Disk Utility on your good working Mac then select the troubled hard drive. Click the repair button; DONE! That will solve your problem. No reinstalling no OS or reformatting anything nor using TimeMachine… BTW, once your problem is solved backup or clone your now working Mac. I prefer cloning. I hope this helps you, peace!