I updated my computer yesterday and now whenever I turn on my computer a pink screen with green lines shows for a second, why is this happening.

In addition, after the initial start up..... my screen remains gray with nothing else happening or loading. I waited for an hour and nothing happened last night, so I shut it off and unplug the thing. I started this morning with the same green screen with the Apple icon inside of a box? What a mess it’s not moved on beyond the gray screen. Don’t know what is happening with Apple the iPhone is just as bad with the new updates 11.1.1 asking now to go to 11.1.2 the phone is slower than molasses.