Hi Van,
I think installation can be very sensitive to reloading pages and the like. You have to be very patient while going through the initial screens, some of them can take a while to load.
Since this is a new install, rather than trying to debug the problem, you don't have much to lose by recreating the database as follows:
dropdb
createdb
createlang pgplsql
Then start the installation sequence again, waiting patiently for the pages to load. Also, double check that there weren't any additional instructions to be followed on the first screen, which is sometimes the case if certain things haven't been properly configured.
Good luck!
