Mac is shutting down and partially restarts with red apple

As i was deleting e-mails my Mac desktop shut down. When it restarts, it has a red apple appears. The loading line appears, in red as well, below the apple, loads 3/4 of the way and shuts down again. It does this over and over until I unplug my computer. I did receive an e-mail last night that said to open in dropbox. It was open in my preview window but I did not open it in dropbox, I figured it was a virus. Sine it won’t fully restart, I can’t try any troubleshooting.

Thanks