I reassigned some key in the configuration menu, and now I am unable to select any menu or even exit the game as it seems the enter key (or *any* other key) do not seem to correctly be bound to the confirmation. I sent a message to GOG support but I fear I won#t get any answer.

I tried pretty much all key inclusive shift , control, alt. Nothing confirm/goes into the menu.

Does anyone know if there is a config file I could edit ? I even tried a reinstall but it does not work.

OK in case somebody got the same problem here is the solution :
Go into your user directory (c:\users\Yourusername in windows 8)
The appdata
the roaming
then watermelon
the piersolar.

There is a pshd.cfg file : rename it to pshd.old et voila the game recognize the config is gone and make a brand new file with default values.

So if your windows user name was SuperGamerlicious

then rename the file
C:\Users\SuperGamerlicious\AppData\Roaming\WaterMelon\PierSolar\pshd.cfg to phsd.old