Why won't Start Up Repair work?

I was using the internet on my computer ( Windows 7, DELL ) and the security shield showed up on the bottom flashing yellow and I clicked it and it asked to allow or deny something with "Setup" in the name and I hit yes without thinking and then 5 seconds later my computer restarted and it keeps bringing up this " Start up Repair" and it won't actually start up. What the heck did I do and how can fix this?