Newbie Issue

Good morning from Australia.
I have a limited amount of experience with cameras and have normally just used auto settings on cameras I have owned and therefore I may ask some dumb questions so apologies in advance.
I purchased a BMCC4K second hand for a reasonable figure or so I thought. Batteries were flat so purchased in good faith.
The following day I put both batteries on charge and waited all day to use.
When I put the batteries in the camera it powered on and showed a green indicator beside switch. The screen on the rear came on and i could see an image clearly. Using a 12-35 lens.
did a factory reset via menu and amended dates and times. I put the AC Power attachment in and it is showing on screen. Running 6.6 so am downloading an update
30 minutes later I switched the camera back on and the back screen was black but the surrounding details visible around the screen.
No image of items in front of camera are visible.
Yes I have all the caps off.
All I can see on screen is psychedelic pink and green splotch.
Have I bought a dud or am I doing something wrong.
Thanks in advance
I have a limited amount of experience with cameras and have normally just used auto settings on cameras I have owned and therefore I may ask some dumb questions so apologies in advance.
I purchased a BMCC4K second hand for a reasonable figure or so I thought. Batteries were flat so purchased in good faith.
The following day I put both batteries on charge and waited all day to use.
When I put the batteries in the camera it powered on and showed a green indicator beside switch. The screen on the rear came on and i could see an image clearly. Using a 12-35 lens.
did a factory reset via menu and amended dates and times. I put the AC Power attachment in and it is showing on screen. Running 6.6 so am downloading an update
30 minutes later I switched the camera back on and the back screen was black but the surrounding details visible around the screen.
No image of items in front of camera are visible.
Yes I have all the caps off.
All I can see on screen is psychedelic pink and green splotch.
Have I bought a dud or am I doing something wrong.
Thanks in advance