Orphan,
It really does seem that the problem is the little battery inside the case. How brave are you? If you take the case apart you will see it on the board, a largish watch battery held in place much like it would be in a watch, and the same delicacy required to remove it. I would go to the expense and take it somewhere to have it done BUT FIRST make a simple program (sadly there's no default pgm stored in it)to make sure nothing else is wrong:

FIRST check the 3 switches on the back, they should all be DISABLE;then press PROG/PARA and 2 more pairs of digits will appear. Select parms with the keypad&adjust them with the up/downs.
1) any one of #13-16 = 1
2) DCO 1 level (#17) =31
3) VCF cutoff (#41?)=about 49
4) DEG1 brkpt (#53?) =31
5) DEG1 sustain(#55?) =31
I don't rem all the parm#s cos I've got a mkII instead- but you should get sound which will vanish when you turn the power off.When you get the new batt. look for patchbanks, they're around. In the US try Kid Nepro in N.Y.C. www.kidnepro.com Enjoy the Poly,you've got a good friend.mn