I use Avast! for years and I never had this problem before.
On this PC I had Avast running before, but since I reinstalled Windows, whenever I install Avast!, after first shut down or restart computer is not able to boot (startup failed). System restore just before Avast! helps.
I reinstalled Windows multiple times, and still no luck.
Right now I cannot use Avast on my PC.
OS: Windows 10 Pro
Laptop PC: Acer Aspire VN7-571G-55BL