Hi ebichan24 and welcome to the forum.
What is your OS?
What product of Avast are you using?
When you installed Avast, did you uninstall it using the Avast Uninstaller Tool in Safe Mode then reboot prior to reinstalling it? If not please use this tool:
http://rejzor.wordpress.com/avast-cleanup-tool/ - it is the Avast Uninstaller Tool with something to get rid of remnants.
What other security software do you have on this machine now and in the past (antivirus, firewall, resident and on-demand software) and how did you uninstall them?
How do you connect to the Internet? Are you having problems with surfing or just updating with Avast? Are you having any other machine problems?
Is there anything in your firewall (FW) that is blocking Avast? What is your firewall?
Sorry for all the questions, but this will help us trouble-shoot better. Thank you.