RE: Business central demo web client issue
Agreed with Steve, windows event logs and confirm file will tell us more.
It could also be a permission problem, when you installed it, were you full administrator on those machines?
Have a try uninstalling unless already did and right click - run as Administrator on the setup file when you run it.
Also install SQL management studio and check if you can see the SQL server, database, compare with your config file. Ideally check if your user is added in the right permission tables.
Alternatively look out for freddy's blogs on business Central containers and install it in a docker container. That might save you time for your project.
Cheers,
Robert