Non-Responsive F9000 Smart TV Logo

[JHUK74]

Hi,
UE55F9000STXXU tv which is out of warranty bought 2nd hand (no returns) but was missing the cable between the TV and one-connect box.
I therefore bought an official Samsung Cable Signal Coaxial Black - BN39-01815B which fits.
However, when I connect together, the TV just shows the SMART TV logo (holds and then fades in and out)
If I plug an ethernet cable into 'one connect' then the screen go's completely black.
Remote control is unresponsive (light flickers so is communicating).
Is it faulty one-connect box?
Incorrect lead (even though it fits)?
Firmware/software?
Samsung support say one-connect box but they have been pretty useless and couldn't even give me the part # for the lead.

As a side issue (as I cannot see how they are related), the power "on" behind the tv allows me to turn on the TV, but it wont turn off using it.
The remote is unresponsive so I have to turn off at the mains.
thanks for any help
John