AVAST 5 cause a blue screen of death in my PC why? how does it comes… 
Why does the sun shine?
Sorry to be harsh, but there isn’t anywhere near enough information here for anybody to help you. According to your post you have a computer with Avast on it and nothing else…
What else is in it? Hardware, Operating system, other programs, even Avast version.
You say in your sig that you do troubleshooting, so you should know what’s required for others to help you.
HTH, Gizbar.
HI emantoyaks,
What is your OS and avast 5 specification?