Desktop log in start up
My computer shows Apple icon with half the bar below already showing loading, then it shuts off starts again and once completed shows mouse icon and keyboard and nothing else on screen, I can't get log in screen
Try resetting the NVRAM per the directions in How to reset NVRAM on your Mac and if that does not work, try to restart in Safe Mode per the directions in Use safe mode to isolate issues with your Mac - Apple Support.
If neither work, please make an appointment to your local independent Apple Authorized Service Provider as you likely have a hardware failure.