Your sample data import is incomplete now. Pls keep on importing sample data until you get “All done . Have Fun!” message.
And then you need to set the home page – front page – in Reading -> Settings and set the menus in Appearance -> Menus tab.
Instead of retrying, pls check the error log. It can be seen in cpanel or you can also check the root directory of wordpress installation. Looks like there is an issue with server setup – probably a missing library or lack of memory allocated. Also enable WP_DEBUG in wp-config.php and see if you see any error when importing. Since the error is occurring even when I do not check “Import Attachments”, the issue is probably a missing library and not memory issue. Pls contact your hosting provider to rectify the issue.
The theme itself is not the issue here since the same issue occurs even with the default twenty fifteen theme activated on your site. It simply fails to import anything. Some server configuration needs a fix.