OS X :: Time Machine Crashed Computer Now It Won't Start Up?

My roommate just lost his data, so I realized I needed to back up. I plugged in an external hard drive (it was an internal that we put into casing bought from OWC, if that matters). I wasn't thinking about Time Machine but it displayed a message, so I said yes, backup onto the hard drive. Then while it was backing up I was just reading a document, the machine crashed. I swiveled my desk to get something and this caused the external hard drive to fall, for a second it was dangling from the USB. (I'm not sure if that's relevant but.)

I first restart (held down the power button), since nothing was happening. At that point the hard drive was making a weird rhythmic clicking sound. Then it wouldn't start up! I tried this twice. Blank gray screen. I reset the PRAM (was that a bad idea?) and when it started again, I get a folder icon with a blinking question mark, over a gray background. Then I freaked out because this was what happened to my roommate, so I haven't touched the computer since.

What could have gone wrong? What to do now? (Local help centers only open on Monday..) Is it worth it to take a train for an hour to go to an apple store right now?