Im guessing it will be the Boot order in which your computer is selecting (its running other drives before the drive you have the cd in, causing the cd to load later than the screen you need to reformat).
F12 = Boot Menu appears in the upper-right corner of the screen when the computer first turns on
Press F12 key, and select your CD Drive (which has the Windows or Recovery disc in already)
If it doesn't boot from the drive, either the CD is damaged (scratched; dirty; warped), or the drive is faulty
keep me updated because i always get this problem and forget how to fix it everytime i reformat