Avast 7 doesn't launch at startup and make windows freeze

Hello. So here what happened.

Yesterday, i upgraded from avast 6 to avast 7 internet security, then rebooted. Everything went fine. I then shutdowned the computer. Today, i boot, arrive on the desktop, and then, nothing. I can’t do anything at all, just move the cursor. And after a while, windows freeze.
The same problem happened 2 weeks ago, and i figured out, that avast was the responsable.

Here’s what i got in the windows event viewer :


The following boot-start or system-start driver(s) failed to load:
aswSnx
aswSP
aswTdi
Wanarpv6
and many others services

I rebooted in safe mode, put the “avast antivirus” and “avast firewall” from the windows services from automatic to disable, and after a normal restart, windows started successfully.
Repairing avast did not fix the problem. I had to uninstall-reinstall.

So does someone know why avast crash so suddenly ? and how to prevent this ?

Thank you ^^