The Yamaha corporation is known not only for its concert grand and baby grand pianos, but also for the electric pianos it produces under the Clavinova imprint. You can find Clavinovas, which are synthesizers capable of producing wide ranges of sounds, in churches, malls and concert halls all over the country. If you use or maintain a Clavinova and find it's acting up, a number of troubleshooting options can help you attempt to fix the problem yourself before contacting Yamaha.
Make sure the Clavinova is plugged in if it won't power on. Although this might seem obvious, it's possible--particularly if the Clavinova you use or maintain is set up in a public place--that someone might have inadvertently unplugged it.
Adjust the volume and check the auxiliary jack to make sure no headphones are plugged in if the Clavinova doesn't make a sound. It's possible somebody has been practicing alone or otherwise trying to be quiet and simply didn't leave the piano the way he found it.
Test other synthesizer sounds if one or more of them doesn't work. If, for example, only the "Harpsichord" setting is faulty, there may be a problem with that individual file. On the other hand, if you can only produce sound using the "Grand Piano" setting, there may be a more serious problem with the Clavinova.
Press keys adjacent to any that are giving you problems, whether you're having issues with intonation or volume or certain keys simply aren't producing any sound at all. If an isolated section of the keyboard is malfunctioning, it's possible a spill or other accident caused the problem; if keys throughout the Clavinova's range are faulty, there is likely a more serious problem.
Contact Yamaha support directly if you can't fix the problem yourself. Point your browser to the link listed under Resources, fill out the form and wait for a response.