First, install the latest version of Lightroom. 5.6 just came out this week:
Second, we do have chat support: Contact Customer Care
Downloaded , installed, reboot machine ... same nice little dialog box pop up saying there was an error occurred when attempting to change modules
I am the only user in this iMac (hence admin level)
Also whenever I started Light Room -- it ask me to register with the serial number ... even thought I had entered it so many times
Tried the Contact Customer Care link you provided .. it link me to the same webpage where I am pretty much left all by myself .. am I missing something here ??
Just because you are the only user on the computer doesn't mean you are the administrator.
Also, the fact that you are being asked to re-enter your serial number each time you start means that it is not being remembered because something is either preventing it from being written to you disk or (less likely) something is erasing it. This does suggest that you lack certain permissions to make changes to your computer. Not only to save your serial number, but to have access to the Lightroom files needed to change modules (they are just plug-ins within Lightroom).
Try creating a new user account and run Lightroom from there (making sure that it is part of the Administrator group).
To get to chat support, you have to choose the options: