A couple of days ago I noticed my computer's wallpaper had changed to warning about something has infected my computer, when I leave my computer alone for about 5 min I get a blue screen saying something has been installed and windows is restarting and I don't remember installing anything in my computer recently (I am pretty sure someone was using my computer when I left for the day). I have malware on my computer and it works but as soon as I open my internet I get pop ups and its right back on my computer. Now when I go on the internet nothing happens my homepage comes up but no links works nor can I go to any other website. Please let me know how to get rid of this, I have tried restoring my computer and there's no other dates besides today.

I need help!!!

Thanks!!