My advice, open the forum and stay out of that section, it's for advanced maintenance and not all tools are as friendly as allowing you to just back out.
You backed out of the rebuild, and THAT rebuild tool does steps incrementally, so it will not process further as additional redirects aren't instructing your browser to issue additional sets of instructions.
Short answer: Your forums are only closed because the rebuild closed them and can't complete the task and turn them back on as you closed the tool.
These are advanced maintenance tools that should be run to completion, and only when you know what you're doing... It is directly maintaining your database...