Avast is turning off my pc

After i turn on my PC it gets super slow, Avast consumes 100 % my CPU and then it turns off. It happened 2 times already, the first i thought it would be and eventual problem, but now i’m getting worried. Though it still seems sporadic, it has happened 2 out of 4 times.
If anyone is having this problem and/or know how to fix it, tell me, please.

What os/sp?
What exact version of avast?
Any other security (related) software installed? (or had previously)

I use windows 7 ultimate 64 bits, i believe it’s the latest version since i’ve installed it 4 days. And i don’t have any other security software installed.

Click to uninstall avast then choose change on next screen, untick NG - complete and reboot.