Window on my laptop won't start

Hey my window is not starting since yesterday, there was some viruses that comes after installing a random software from untrusted site. My laptop is new i just got it last month, it's in windows 8.1. Last night i install a admalware software to resolve issues but after that all when my laptop restart it won't be on just a black lighted screen appears. When i start my laptop as usually it goes to the password screen and afterthat i enter my password then it goes to the black lighted screen. Please help me to solve this issue