Stuck at boot after longer period without batteries/power

Hey guys
I encountered the following problem, not sure if it was discussed somewhere already.

I had the reform lying around for some time, battery packs disconnected, since the batteries drained too much from me not using the laptop regularly.
Common mistake, discussed here a lot.

Anyway, I bought a new set of batteries matching the original delivered ones and now the reform is back to life but stops doing anything right after the boot splash screen.

Any suggestions or did someone encounter similar behaviour?
Pluggin in a usb device gives a response (device data)

Many thanks for your thoughts on this

Edit: still on original firmware