Help! Screen goes black!

Hello,
Last night I shut down my acer laptop while windows vista was updating. I shut it down by holding the power button. Now when I start it up it comes up with a screen giving me two options. One is start up repair and the other is start windows normally. I go through the first option first then the secong and when I go through the second the screen just goes black but it is still running. I really need help because my parents will kill me if they find out.