Preview on macbook pro not responding

1 Problem became 2 headaches. I have a brand new MBP 15", 2017. on a macOS High Sierra which I installed when I received it. Version 10.13.4 Top of the line with 16 GB memory and 512 SSD

I was copying photos from pexels.com and one of them is embedded on my Home screen in Preview mode. That's been there for approximately 10 days and I've done nothing to try to fix it because I haven't a clue where to start.

Just tonight, I got a hang-up telephone call on my iPhone and the message flashes on my MBP screen in top right corner. Message gives me a choice of 'Accept' or 'Decline' [next to the 'Decline', there's a drop-down menu giving me a choice to 'Remind me in: 5 minutes, 15 minutes or 1 Hour'. No matter what I do, it does not respond. So now I have 2 UNRESPONSIVE Messages after closing down everything else.