Most often, when your flute, clarinet, saxophone, oboe or bassoon won't work properly, air is probably leaking from one or more pads. Usually the leak(s) are small and very hard to detect. Sometimes you can actually see a spring that has become detached or can see a pad that won't open or close easily.
One way to pinpoint the problem is to slowly play a descending chromatic scale from some open fingered note. As you go down the scale, you may be able to notice when the problem becomes apparent. Often times, your problem is some leaky pad above the topmost open hole.
if it's a detached spring, you can probably reattach it. If it's something you can't get to, or aren't sure what to do, get in touch with a repair technician.
Just to be safe, if you are in doubt about messing around with your instrument, leave it alone. You don't want to make the problem worse than it already is.
If you live on the North Shore in the Salem area, give me a call.