I have a lenovo legion y520 laptop,I want to download sth from the Internet but the anti-virus won't let me download it so I delete the ani-virus, after that my hdd 1tb disappeared from the laptop then the laptop become too slow when I want to turn it on , and some times the screen stays black and I can't see anything , I don't know what the problem exactly but I think it's a virus, can anyone please help