A couple months ago, my MacBook said to replace its battery. I put it off until recently & now that I have it won't go past the logo & alternates from blue to a white screen that has the loading spiral. It does this over and over again.
MacBook
Mac OS X: Gray screen appears during startup
Symptoms
Instead of seeing the Finder or the login window after startup, your computer may stop responding and the display may only show a persistent gray screen (you may also see an Apple logo, spinning gear, spinning globe, prohibitory sign, or a folder with a flashing question mark on it).
This usually means it cannot find an operating system, but there are many more troubleshooting steps to follow in the above link.
Boot from your original System Install DVD or OS X Recovery, depending on the version of Mac OS X you have.
Similar problem on my Macbook 13" that I fixed with a SMC Reset. Unplug the power supply and remove the battery, then press and hold the power button for 5 seconds. Replace the battery, plug in the power supply, and power up.
Hope this works for you :)
MacBook won't start up past logo & loading spiral
