I was downloading avast antivirus

Question

i was downloading avast antivirus and after restarting and scaning between that time i was a little busy so when i finally look at the screen it was black so i was thinking that it was screen saver so after touching one or two keys and waited for sometime i hard to shut it down manually and restarting it, it recommended that i should be booted thourgh repair which i did but after that it could not connect to the internet so i have to go the devic manager then there was a yellow sign at the mircosft 6to4 adapter so what can i do