I recently got a PT-20 that had the same issue at first after cleaning leakage from batteries that expired 21 years ago, with the exception of not responding to any keys or buttons. I don't remember if I tried the reset button. For the first time testing, I did use 4 Eneloops and one Energizer rechargeable AA (all were fully charged). I opened it to inspect for damage, and found the boards to be miraculously unharmed from the battery leakage – the foam pad on the battery door was the only total loss. I didn't see anything obviously damaged on the inside, so I put the batteries back in to check voltages. This time I had found another Eneloop, so I used all Eneloops, and it worked perfectly! I don't know if it just had an odd reaction to the one Energizer, it needed some extra persuasion to wake up from its quarter century hibernation, or opening the case moved something to make it work, but that was a surprisingly easy fix! Though it does still have a slight hiss in the background.
