Success!
You were ABSOLUTELY right!
There was a faulty D2. Removed and everything is working now!
FreeZinG is D2 for ESD purposes? Has it to be replaced?
Note: In order to remove D2 you must have access to the second PCB (with mini usb plug).
You have to unsolder 4 pins near the usb plug and two other pins on the other side.
BE CAREFULL not to heat too much as you can easily destroy tinny pads! (guess how I know it 
) I managed to destroy one of the usb Data lines BUT I repaired soldering a tiny wire from R22 to mini usb pin.
I am happy DSO is working again!
Thank you for your advice FreeZinG
also: As I am going to try out the 3rd party fw by Paul, in case I want to revert back to original file , could we have the fw 2.01 comes with dso ,please?