Test your AC adapter to ensure that it is still properly providing power to the PX-700 battery. Remove the battery from the back of the PX-700 and plug the piano into AC power. If the PX-700 powers on with the battery removed, then the AC adapter is functioning properly. If the PX-700 does not power on, then it is likely that the AC adapter is broken or malfunctioning.
Contact Casio Support for troubleshooting assistance. You should also inquire about the status of your warranty, as you may be eligible for free service and repairs. If you are eligible for free servicing, you can inquire about certified Casio technicians in your area, or arrange to have the piano sent to Casio.
Contact the Casio Parts department directly by calling "1-800-223-2001." You can order a replacement battery or AC adapter directly from Casio or inquire about local vendors in your area.
Remove the malfunctioning battery from your PX-700. The battery is located behind a plastic cover on the back of the piano body. Fit the replacement battery in place, making sure that the negative and positive contacts on the battery are properly matched up to the contacts of the battery compartment.