White Screen :P

So i have bootcamp installed on comp and i switched to mac for a while but then when i shutted it down and went on the next day it didnt work. Usually when i try to go on my mac i have to press alt which would give me a menu of the start up disks available but now when i do it all i get is a white screen. So i put in my iMac restore disk and tried to run it form cd by pressing C during start up WHITE SCREEN. wat now? every command i try always becomes white screen