O.k then right now this could get tricky , if this unit was not working when it was stored then anything internally could cause this .
If it was working then perhaps we could be talking about dried up/vented caps that do not like to be left unused for extended period and who may just come back to life after a few days being powered but I would not count on that too much .
Right now the only thing I could offer is the reset procedure and if that doesn`t work then it would mean repairs and I`m sorry but this type of repair has to be done hands on , I cannot possibly guide you through the circuitry from here .
Here is the reset procedure and then I will opt out and repost your question , I posted here by mistake anyway .
1 Switch off the unit and remove the AC cord from the wall
2 Hold the following SPEAKER A button and B button, and plug
the AC cord into the outlet.
3 Check that the entire display is flashing with an interval of
about 1 second, and release your fingers from the 2 buttons
and the microprocessor will be initialized.
• If step 3 does not work, start over from step 1.
• If the microprocessor has been reset, all the button settings are
reset to the default values (the values set upon shipment from