That’s almost certainly due to a PHP error, and errors are not being shown in the browser on your host. I suspect something in config.php is amiss. Can you post the config.php, or look for these common errors:
strings must be quoted (like your akismet key if you entered one)
your domain name, home and siteurl must all be quoted (due to slashes and colon)
possible problem with the table prefix for bb or wp?
If you have a command line at your host, you can also check the syntax of the config.php file by running:
php -l config.php
No syntax errors detected in config.php
that’s a lowercase L after the php
Post your config (edit out the good stuff) if you need more help.
If you get a huge page with something on it with loads of information then you have windows installed. Just looking at your 404 pages show that you have a windows server – low change of having php more likely to be asp.