I know I'm a computer idiot but does my laptop have to go against me as well? *kicks*

Does anyone know what to do when you try to reformat your laptop & it decides to be really cranky & restarts continuously? Like, I get the Acer logo thing, it flashes, I get my Window XP which is loading, it flashes & goes back to the Acer logo thing, & then the Window Xp thing. Continuously. & it doesn't help if I press the restart button or when I switch it off & on again. Help help help.