Viruses after updating

I saw an update for mcaffee pop up on my screen and I said I wanted to install it.
So after I installed it and restarted, my computer said it had some sort of trojan.
I try to access my control panel and everything else on my computer, but it won't let me click on anything, just a message pops up saying I have a virus.
How do I get rid of this?

Thank you in advance!