Air-O-Swiss is an upscale brand of humidifier that creates a fine water mist, instead of blowing air through a wick. Unfortunately some models are prone to problems. One problem a number of people have encountered is a humidifier that no longer produces any mist (e.g., here).
If you have an AOS 7144 or similar model that no longer produces mist, and your warranty has expired, Air-O-Swiss may tell you there is no solution and you have to purchase a replacement. If so, don't give up hope! It is possible to revive a non-working humidifier and get it to produce mist again. This Instructable explains how.
Note that this Instructable assumes a moderate skill level. You should be comfortable using hand tools and a soldering iron, and be able to disassemble and reassemble moderately complex equipment. Opening up your humidifier will probably void your warranty, but if your unit is under warranty you probably wouldn't be here in the first place!
While making this repair and using the repaired unit isn't a dangerous activity for a moderately skilled person, obviously I disclaim all liability resulting from your use of these instructions. I can't be responsible if you burn yourself soldering, or if your unit ends up catching on fire, etc. Proceed with caution, and if you're not confident in your ability, seek the help of a qualified person.