My 60 day trial has run out, and I’ve tried to get a registration key, but the page doesn’t work for me. I’ve had people give me a link to it, I’ve typed it in myself, I’ve googled it and clicked a link, but the page never shows up. It just says ‘Internet Explorer cannot display the webpage.’ Any suggestions??
Welcome to the forums, alicherie. 
Is this the link you are trying?
http://www.avast.com/eng/home-registration.php
Try this one - SSL Registration Page: https://secure.avast.com/scripts/register.php
Or this one - http://67.228.112.194/eng/home-registration.php this is just one of the IP addresses for avast, as some malware can modify the HOSTS file to stop you getting to security sites such as avast.com. By directly using an IP then it would avoid that hack, so perhaps you should try this one first.
Is this occurring only with avast or other sites are with problems too?
Isn’t this computer infected?