Macbook turns off during start up

[SR 7]

My 09' Macbook turns off on its own during the screen where it shows the loading bar at start up! It turns off at about the point where is the bar is showing about 70% complete.

Is this a battery issue because I had my macbook off for a good 6 months without turning it on and it does need a new battery to begin with so I am not sure if this is an OS issue or the battery isn't strong enough to push through the rest of the way?

 

[adrianlondon]

If it's plugged in, I wouldn't think the battery would have any effect on the bootup.

 

[DeltaMac]

More often, the hard drive will fail tests during boot. It retries the test a couple of times. If the hard drive still does not pass, the Mac shuts down.

 

[SR 7]

Any idea on what to do then?

 

[DeltaMac]

You can try booting to your recovery partition (if you have Lion or higher) by restarting while holding Command + r
You should boot to a menu screen, where one of the choices is Disk Utility.
Choose that, and then select your hard drive, and click the Repair Disk (or First Aid) to run a quick test of the hard drive.
If that fails with some kind of error, then it's likely that the hard drive needs to be replaced.
And, that would be your next step...

If the Disk Utility doesn't show any issues with your hard drive, then your can Quit Disk Utility, which will return you to the menu screen. Good next step might be to Reinstall OS X.
If there is still a problem with the hard drive, the reinstall may fail, and you can proceed with the same step again (replace the hard drive)

 

[SR 7]

So I ran disk utility first aid on every single one that had that option and they all passed but 1 which I believe is my main one.

I had backed up my HD a long time ago on an external HD.

If I connect this external back up to my new macbook from the USB port, do I have access to it as if it was my old mac?