It sounds like your ROM battery, which the ROM contains and stores the patches for the keyboard, has gone completely dead and your keyboard is dead in the water. However, if you can get a MIDI to USB converter and get the battery changed, then you can reload the patches back onto the keyboard.
I have worked on a Korg M1 Workstation and have had to replace the battery(CR2032) and then had to run a program called "MIDI-OX" which also gave me access to the patches needed in order to restore the keyboard to factory patch settings.
Take a look at this AFTER you have gotten the battery replaced. I will tell you that replacing most batteries is a very intricate job as, the bottom of the keyboard has to be removed, as well as a lot of the internal boards. I had to draw a diagram and mark certain pieces so I would know where they went and in what order they have to be re-attached. My advice is take it to someone who works on electronics unless you want to DIY (not recommended) to get the battery replaced.
Hope this helps.