MacBook won't boot on Yosemite after force power off Macbook suddenly froze while I was using Google Chrome so I waited for 15 minutes hoping it would un-freeze. After 15 minutes, I decided to force the power off by pressing and holding the Power button. When I tried to turn it on again, I heard the chime, but the screen remained white, and the hard drive started making clicking noises. 

Model identifier: MacBook6,1
OS X 10.10 Yosemite
Hard drive clicking/clunking/scraping noises (other than the usual sounds of an HDD in operation) are nearly always a bad thing and it's best to assume it's terminal.

If it is your hard disk (or if you've ever erased/replaced the disk) you won't be able to access the hardware test, in which case you will need to start your MacBook with the Applications Install disc that was supplied with your computer.