Unexpected shutdown and now won't restart

In the past couple of weeks I have experienced an unexpected shutdown. It started when I was in Skype. And when it occurred, and I restarted, it would run a couple of minutes and shut down again. I researched the issue A couple of days ago and saw a fix suggested. I was to hold down the shift control and option keys on the left side of the keyboard while also pressing the power button. I just press them altogether and let off. After that my MacBook was back to normal. At least I thought so. I was on Skype again today and it unexpectedly shut down again. But what is different this time, is now I cannot get it to boot back up. It makes the opening chord sound and I can see the white Apple logo appear for just a second and then it simply stops. If at some point I am able to start my MacBook I will delete Skype. But if I still have issues after that, what else can I do to fix this?