That sounds like a virus to me. Can you boot up in Safe Mode and then try your antivirus again? You could also try another antivirus approach. I've had good success with the free version of Malwarebytes Anti-Malware.

Here is a link that might be useful: Malwarebytes

that is an infection, you will need to get it cleaned up. If it will allow you to get malwarebytes free, update it and run full scan and let it clean what it finds, then come back and post your log so we can see what infections you had and know how to proceed.

Do not click on anything on the screen with that warning, reboot your computer to get rid of that screen.

Here is the link to malwarebytes.
Malwarebytes' Anti-Malware

I think you need to reformat your pc.

same thing happened to me several years ago....find whatever is new in your desktops file that you know you didn't intently download....I was infected with a form of malware that changed my desktop to appear like I had the dreaded blue computer screen of death....and eventually, it probably would have infected it enough to make me scrap it...just do a search for whatever you find that is unusual, worked for me! and now it's still clicking along years later!

Years ago it was a fairly simple task to remove a virus. today with the myriad of virus, Trojan and Rootkits things have become much harder hence the need for more vigorous protection.

Just yesterday I cleaned a computer with over 150 infections, 66 of those were Rootkits. Many were harmless cookies too. The owner had scanned with Superantispyware just 5 days prior so it did not appear to be neglect although there was a peer to peer program installed.