Have left my FX-CG20 without batteries for a couple of months, I put 4 new AAA in.
it boots to the Languages screen with the cursor at ENGLISH.
None of the keys do anything a reset just brings me back to same screen
Any ideas anyone?

It sounds like you may need to re-install the OS. I found the OS for your calculator on Casio's website here. It looks like it comes with a guide on how to send the OS as well. Good luck!

Thanks - I’ve tried to connect it to my laptop but it doesn’t show as a drive. That’s connecting with the USB cable. I seem to remember the other (Jack lead cable) is for connecting 2 calculators together?
I’ll try and download Casio software tomorrow to my laptop to see if it can ‘see’ the CG20.

I also have a fully working FX-CG50. Is there a way I could port the OS from CG50 to CG20 if I connect both calculators using the supplied jack to jack cable?

This will be difficult to do if at all possible and too dangerous to try - 50’s OS shouldn’t run 20’s model

Still getting nowhere with my FX-CG20. At power on it’s just stuck on the language screen with the cursor still at English. As stated none of the keys do anything when pressed and neither my Mac or my Windows laptop ‘see’ the calculator as an external USB. One thing is interesting in that the calculator, when it was working, should ask for a User ID and password - it doesn’t anymore and I’m wondering why it’s going straight to the Language screen? I keep coming across references to key combinations to hold down when booting the calculator - does anyone have a definitive list of these please?
However at 72 with chronic Rheumatoid Arthritis some of these combinations would be challenging to an Octopus - e.g. hold down reset button on back whilst holding down F2 4 AC/ON then release reset button, release AC/ON after 2 seconds, release F2 and 4, wait 2 seconds press 9 and then X (multiplication)!!! I think Casio technical should get the ‘Most disability award’ Nobel Prize for coming up with this combination!!! Haven’t been able to try it - I’m on the mega COVID-19 shielding list for the UK so nobody to help me press the keys!

Regarding combo keys - I found it hard every time too. One thing I remember doing was having one of the batteries half out and reinserting it at an appropriate moment instead of doing any reset button presses

Having said that, is it perhaps possible that your keyboard is malfunctioning like up down buttons, exe etc not working or perhaps an exit button is stuck or something similar disabling the rest of the buttons...?