On 16.04, 18.04 and 19.04 - on a Xeon Workstation, the OS on an SSD with a Firepro V4800 graphics card. "Cold" starting my PC after the grub beep if enabled - I get a purple screen for up to five minutes or so but usually around three or four. Ubuntu then starts.
If my PC hasn't been switched off for more than a minute or two - it boots at at normal speed.
I have been going around in circles trying the solutions Googling offers to similar problems, with the exception of rolling back the kernel.
Any help gratefully received. Many thanks.