I have a TI Nspire CAS Touchpad calculator which sometimes works normally but sometimes seems like it's dead (doesn't do anything when ON is pressed). Sometimes the calculator also makes strange noises instead of starting up when I switch it on, but after removing a battery it works normally again.
The keypad and the battery aren't the problem, I already changed them.

Attached is a recording of the noise it sometimes makes.

Does anyone have an idea if I can somehow fix it, or what is broken?

I would open it up and see if there are any sign of a shortcircuit or damage.

I've already done that, but nothing looked much different than in a working Nspire Touchpad.
On an unrelated note, it seems to be an older hardware revision than the one that still works, even though they were bought together.

That sound make me think of something like a shortcircuit, I have no idea what could be wrong though. I hope it can be fixed

It made me more of think of the sound an NXT makes when it's in firmware update mode. More the sound of a buzzer than something produced by accident.

Right now the noise is hardly noticeable, I can only tell it's coming from the mainboard and not the screenboard. If it gets louder again I may know more precisely.