Won't start up while running on batteries

Got a problem, I haven't found a solution for yet. Maybe there's someone that can help me out here.

I got an MPC 500, second hand. I upgraded it with the 128 MB RAM from AKAI and it all worked just fine. No matter if running on batteries or plugged into the wall. I then didn't use it for like three or four months. It now does work perfectly well when being plugged into the wall, not so when running on batteries. If I turn it on when running on batteries, all I see is a blank screen. Backlight works, but that appears to be the only working thing. I also tried another set of brand new batteries, didn't change a thing.
I never dropped it or anything and the place I've put it while not using it is not especially humid or any. Also the old batteries that were in it while storing it, didn't leak or any.
Anyone got an idea what else I can try to make it work? thx

no idea, i used the battery a week, then all of a sudden the unit restarted herself **** all my progress up. plugged on the wall since then...
i didn't know there were battery issues

Rule #1 for any battery powered unit is that when stored away for long periods of time, you should remove the batteries. Leaking or not, the batteries are still active and is giving the MPC a charge even when turned off.

I would take it apart and spray the positive and negative contacts with electronic cleaner and brush them with steel wool. Those contacts must be corroded green by now.

Thx for the response! Took it all apart. Even tho nothing seemed to be out of the ordinary, I cleaned all the contacts as advised. Apart from the fact that I now know that I can take my mpc apart and put it back together and it still works (!), it didn't help anything. Unfortunately, the issue remains.
Any other ideas? It obviously don't seem to be a common problem

Have you tried adjusting the screen contrast when running on batteries ?
I know it's a long shot, but worth a go.