Freaky macbook problem -- please help!

just the other day i popped in a dvd and my computer slowed way down before completely locking up. with no other option i pressed power to turn it off. after pressing power again to turn it back on, the usual grey screen came up but with a circle through a line through it (like a no smoking sign) and is freaking out and twitching between that, the apple logo, and a symbol of a folder icon with a question mark on it. I have no idea whats happening and can't get my computer back on.. im writing this from my roomates computer.

please help if anyone knows the problem or has encountered this before.

it sounds like you have a corrupted file in your operating system. Can you boot into single user mode or safe mode?

after trying to boot in single-user mode and vebose mode, the black screen with white writing came said that there was an error loading, and couldnt load "mach_kernel"

any solutions?