Yesterday my Avast still won't update even after a few attempt of reboot, trying to let it update automatically, and forcing it to update.
So, as a last resort before repairing Avast, I turn to ask my friends who use Avast whether they have the same update problem like I do or not. Most reply saying that they have no problem with update. Then, one of my friend telling me to trim my Visual C++ 2008 Redist. installation by keeping the latest version and removing the older version from my computer. I try her advice (despite of how strange it sounds to me) and removing 2 from 6 Visual C++ 2008 Redist. installed in my computer (I remove older x86 which I believe came from Avast installation and older x64 which came from my graphic card driver installation).
After removing those two, I try the manual update and finally Avast start the upload and download activity. The manual update went alright. Today, a few seconds after I connected to the Internet, Avast successfully auto updating itself. So, I guess my friend suggestion work after all and I don't need to resort to repair my Avast installation (and setting it all over again).