Welcome jthomas34,
First let me ask you if you what other security software you have your machine including the version of Avast, firewall (FW), and any other security software?
If I understand correctly, you have 2 machines (desktop and a laptop). Is it the XP-Pro with the problem or is there a different OS with a problem? If the other machine has different specs., please give them to me.
You mentioned that you are getting error codes when trying to update on the laptop. What is the FW on the laptop and is the FW blocking anything for Avast?
You mentioned that you found a virus. Which machine was this on and were you able to quarantine or remove the virus? What was the virus? Sometimes, a virus will prevent you from installing AV software. On the other hand, remnants (perhaps prior version of Avast) from security software will also do the same.
For uninstalling and doing a CLEAN install of Avast, did you follow the procedure I posted in this thread?
Since you had a virus, I recommend that you start a new thread under the forum of Virus and Worms if your virus was not removed and there are people there who deal with virus removal. If the virus was removed, you can start a new thread under Avast 4.0/5.0 Free/Pro and include this thread as a link to your new post. Thank you.