my flute is not playing right?

Please get it to the repair shop as soon as you can, you really should NOT let ANYONE that is NOT a professional repairer to try to fix this kind of things!!

Sounds like they unhooked the spring! Flutes don't have any sort of 'cord' so that's got to be what it was! Make sure the spring is hooked properly onto the little latch. Sometimes if you CAREFULLY use a flat-head screwdriver (maybe have one of your parents do this) you can poke the spring down and back to the side it needs to be on. DO NOT BEND THE SPRING as this will increase the chances of the spring breaking which is about $40 to have replaced!

well since you didn't specify which screw came undone, or at least what part of the flute the screw was located, it is hard for us as readers to analyze the problem. i would suggest you take it to a music shop and have them look at it. they can probably tell you what's wrong and fix it for you. when screws come out the flute is really easy to fix, don't worry, it will be working fine once you get a professional to look at it.