Help! Windows isn't booting!

Okay, yesterday I was rebooting my computer, and for some unknown reason, a sort of error message came up, basically stating that Windows did not start, would you like to... start in safe mode, start with last features that worked, and just start Windows. I've tried all of the options, and (with some minor differences with safe mode), they all came to the same conclusion. Windows would load, but as soon as it finished, the computer would automatically turn off and I would have to go through the whole process again.

Any suggestions?