Ubuntu 19.04 stuck on purple boot screen after install from usb drive on MacBookPro 4,1 Early 2008

Installed Ubuntu 19.04 from a USB drive. Booted into Ubuntu on that USB and installed from there.

Install went fine and after restart was told to unplug USB, another restart and boot is stuck on purple screen.

Likely related to graphics card NVIDIA GeForce 8600M GT.

What can I do, to solve this? Thankfor for noob-proof step-by-step suggestions.

Interstingly booting Ubuntu from the USB drive works fine.

Have no problem reinstalling again. The drive in the MacBookPro can be overwritten no problem. Does it have to be formatted prior to installing or does the ubunto install cover that part?

It’s a bit unclear how to proceed form here.