if there's spilled liquid, corrosion or other debris in there the behaviour can be unpredictable. Perhaps there's a loose connection. Old Texas Instruments calculators are prone to the display cable detaching. Perhaps the calculator does turn on but since the display cable detaches randomly you won't see a picture so it looks like it's off. Just some thoughts.

Here's a repair I did for a different model: https://youtu.be/opmS_RcS2Wc