Are your system well configurated for ‘dial-up’ or ‘permanent’ connection to the Internet?
What do you mean wiht ‘system hangs’? Total freeze? Have to reset manually?
Do you try a manual update? Does it work?
Do you try to desinstall/install avast again? A lot of troubles with updating are solved by this proccess because of some incompatibilities/bugs in previous versions (if I’m not wrong and being unfair with avast!) 8)