Chosen Solution
When in turn on my Mac it shows a startup screen with some weird flashing icons. What do this mean? And how to fix it?
Looks like it is trying to pair with an Apple external mouse. If you have one close, move it to another room. Try starting up in Safe Mode by holding down the Shift key on start up. This could also mean a trackpad failure. Possibly liquid damage. It is looking fora mouse input. Try using a bluetooth mouse with it and see if it will connect.
