System restored computer, reinstall avast?

Hello, I had to do a system restore on my computer today since I kept getting the blue screen and nothing was fixing it (A problem I only had after the newest update to Avast.) I’m not sure if this is actually a known problem or not. What I want to do is reinstall Avast without having to pay for it. How would I do this? And if the newest avast update is crashing computers, then I’d like to know. I love Avast, but I already lost a years worth of data because of that update and dont want it to happen again. I’m using a Samsung laptop with Windows 7 Home Premium.

Thank you.

What I want to do is reinstall Avast without having to pay for it. How would I do this?
you did save your license file?

run this first. http://www.avast.com/uninstall-utility
download and install your program. http://www.avast.com/download-software

insert license file
https://support3.avast.com/index.php?languageid=1&group=eng&_m=knowledgebase&_a=viewarticle&kbarticleid=1084