My Dell Inspiron 15 laptop screen goes black after login

Hello,

I just find that my laptop screen goes black after log in and I can only see mouse pointer on screen.
This was happen when today I was trying to install Microsoft office 2016 software in my laptop and after installing it, it asked for product key at that time I downloaded and try to install KM Auto net software to activate MS office 2016 but at that time I saw that window defender show notification that it can harm your computer and automatically delete it.
Then I search online about product key and I found it and activate MS office 2016 then I shut down my laptop.
After that in the late evening when I open my laptop after log in I found that laptop screen goes black. And I can only see mouse pointer on screen.
So what is problem behind it?
what can I do for fix this problem? Please help me