Firstly disconnecct your computer from external network, if connected. Save the setup files necessary of Anti-Virus and other application in a Pen-Drive. You may need to install during follwoing steps.
1.) Log on yo your computer in safemode. Make sure that you are not connected to any Network. (Even internet)
2.) Now you can unistall the AV. And reinstall it. (I recommend to go for Bitdefender or Avast free version)
3.) Clean your machine with AV.
4.) After, clean your machine using the follwing applications:-
>Trojan remover (Still in safe mode)
5.) Once you done with cleaning your machine, Run CCleaner to remove all temporary files.
Thank you :)