I have an all in one Mac OS X with 2.4 GHz Intel Core 2 Duo processor. When I turn it on the screen is white with the spinning circle in the middle like its powering up but never does. It just stays like that.

Hello
You can check your hard drive's health at startup pressing command-s. you will see a black screen with white text. simply type "fsck -f" and press return. It should check your drive and tell you if something goes wrong with it, and repair it if possible. Then type "reboot" and press enter to test.
It this does not help, you can press the shift key at startup. It does the same thing, but also disables the extensions at startup, this will help you to find out what the problem is. The startup will be longer and it should ask for your admin password.
If this still doesn't help, you might have a hardware problem (hard drive). You can try to backup your data, erase the disk and reinstall the system. To backup you need another Mac, and a firewire cable. Press the "T" button at startup, this should set the Mac in "target" mode, allowing you to use it as an external hard drive. Then connect the firewire cable between the two macs. On the mac that is OK, you should see the hard drive icon of the other mac...
Hope that you will succeed and that it helped you someway