stuck at gray loading screen..

[tweakk]

okay here's what happens:
I turn on my mac nd it loads the gray screen. then icons start flashing, the apple icon, the question mark in folder icon, and this cancel icon thing keeps flashing. when i press cmd + s i get:
boot file path: \System\Library\CoreServices\boot.efi
.Loading kernel cache file 'System\Library\Caches\com.apple.kernelcaches\kernelcache.2B16A4B0'
Loading 'mach_kernel' . . .
Could not open file 'mach_kernel'
Error loading kernel 'mach_kernel' (0x8000000e)

idk what happened. help please :]

Thanks a bunch :]