password screen when opening os x recovery

I have a school provided Macbook Pro which runs OS X Yosemite if I'm not mistaken. Earlier today it suddenly froze up on me, and so I restarted it, but then it showed the flashing folder with a question mark each time I booted it up. I looked up on my desktop computer how to fix that, and Apple's website told me to hold Command+R when I hear the startup sound, which it says takes you to OS X Recovery. But when I did that it showed a password entry screen with only a lock icon, an entry bar, and a forward arrow button to the right of it. I tried some passwords I know, but it didn't work, and I assume it's a password only my school knows. I looked stuff up on that password screen but didn't find anything. Is something wrong with the computer, or should I just take it to my school so the people there can enter the password?