The setup.log holds cumulative information on your updates, etc. so it looks like it has grown very large. This might be a possible reason for problem with the log viewer if it can't load it.
Try going into the program settings, logging and set the Log File size limit to something small, like 256KB you may have yours on 0 no limit. I don't know if this will also restrict the setup.log file as it isn't on the Logging level options, but it is worth a try. I would then suggest you reboot to ensure any changes are applied and see if a) the setup.log is reduced from the 11MB and if so can you open the log viewer.
If the above makes no difference you aren't left with too many choices - but don't do the reinstall without first reporting the results of the logging size change. You may be able to disable the avast self-defence module and then rename the setup.log to setup.log.old and reboot, this may generate a new setup.log but I don't know.
You shouldn't lose your updates, though I'm not sure which updates you are talking about, but it won't effect anything outside of avast. I'm on dial-up too and yes it will take a bit of time to download the 20.7MB, use the link that downloads from avast not from Cnet it is quicker.
http://www.avast.com/eng/download-avast-home.htmlThere aren't many options if something isn't working and a repair hasn't resolved the problem, we/you don't know if anything else might not be working correctly.
So download the latest version, go off-line, uninstall, reboot, install the latest version.