Why wont my mac book turn on completly it just shows the start screen and under the appl theres a bar that keeps loading and when its done it just powers off why is this happening??????

Question

Why won't my macbook air turn on completly just at the start up page and under the apple logo there's a bar that just loads and when its done loading the Mac just powers off this just happens over and over I'm afraid if I do any thing my pictures will be lost on the computer ???

Answer 1

Hi jasonfromforthworth,
Thanks for the question.  If you have updated to Yosemite, then the Apple Logo with the status bar is the expected behavior for when the computer starts up.  However, the powering off is not supposed to be happening ... so here are some steps to take if your MacBook Air won't turn on.
OS X: What is Safe Boot, Safe Mode? - Apple Support
http://support.apple.com/en-us/HT201262
Starting up in Safe Mode
Follow these steps to start up into Safe Mode.
Be sure your Mac is shut down.
Press the power button.
Immediately after you hear the startup sound, press and hold the Shift key. The Shift key should be pressed as soon as possible after startup, but not before the startup sound.
Release the Shift key when you see the Apple logo appear on the screen.
After the Apple logo appears, it may take longer than usual to reach the login screen. This is because your computer is performing a directory check as part of Safe Mode.
To leave Safe Mode, restart your computer without pressing any keys during startup.
Troubleshooting: My computer won't turn on - Apple Support
http://support.apple.com/en-us/TS1367
This article discusses what to do if your Mac won't turn on. To differentiate this from a display issue, be sure that when you press the power button:
You don't hear a startup chime.
You don't hear any fan or drive noise.
There is no video on your built-in or external display
If your computer has power but doesn't display any video, it may have one or more of these similar symptoms when you press the power button:
You may hear a startup chime.
You may hear fan or drive noise.
You may see a light from the Sleep LED (if your Mac has one).
Pressing the Caps Lock key on the keyboard causes it to light. 
If any of these display-related conditions occur, see Troubleshooting: My computer has no video instead. Otherwise, continue with this article.
If your computer won't turn on, try each of these steps:
Verify you have a good connection from your Mac to the wall outlet by confirming the power cord and adapter if present are securely connected and plugged in. To check if the wall outlet is working, plug in a lamp or other electrical device.
If the wall outlet is working and you continue to have no power try another power cord or adapter if available. If it works you may need a replacement cord or adapter. 
Note: See Apple Portables: Troubleshooting MagSafe adapters for further troubleshooting with MagSafe adapters.
Disconnect all accessories that are plugged in to the computer, such as a printer, hub, or other mobile device.
Reset the SMC.
If you are still unable to start up your computer after trying each of these steps, visit an Apple Store or Apple Authorized Service Provider (AASP) for further diagnosis. If you plan to visit an Apple Retail Store, make a reservation at the Genius Bar using http://www.apple.com/retail/geniusbar/ (available in some countries only).Note: Diagnostic fees may apply for issues not covered under warranty or the AppleCare Protection Plan (APP).
Last Modified: Oct 22, 2014
I hope this information helps ....
- Judy