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
What OS/SP ?
What exact version of avast ?
Did you install all drivers and Windows updates before installing avast ?
Is it a clean installation of Windows or a factory restore ?
Windows 10 Pro (All updates). Complete reinstall (format disk). All drivers installed.
I do not know, I just download latest installer http://files.avast.com/iavs9x/avast_free_antivirus_setup_online.exe
Installation finishes without errors.
Try your download from here:
http://files.avast.com/iavs9x/avast_free_antivirus_setup.exe