Korg Poly800/EX800 Users

Hello, I'm new here and have a big problem already. I took my MkII 
out after leaving it in the bag for a couple 
months...and...nothing...almost. No display, no audio, but in the 
phones you can hear a very soft, very slowly rising, self-oscillating 
filter sound. I know the power supply is good cos I can power other 
things with it. Has anyone else encountered a problem like this? I'm 
bummed.Thanks in advance for any help!