I dug deeper to find out whats causing this bug. For XP users who may have the same problem, try going to your System Information, then navigate to Software Environment, then Startup Programs. Look for any other program other than avast5 which calls on the avastgui.exe /nogui command. In my case, it was a Cyberlink software that came free with one of my peripherals and which I barely use. I uninstalled the Cyberlink software, and that fixed the problem. Of course, if the software having conflict with Avast is one that you often use and really need, you may have to decide which software you want to keep. I don't know why this happened in the first place, but I hope this helps other users.
Thanks to everyone on this forum for all your help!