Custom theme won’t load pages/posts

I’ve been playing with creating a custom theme for a company I am working for, I have been able to play with the design and layout of the home page and have entered posts and pages to supplement the home page.

BUT, when I click on a page or a post it brings up a “Page Cannot be found” error. I have also switched back to default (Kubrick) theme and same problem occurs. I do have an index.php, page.php, single.php, etc. in the custom themes directory.

Any ideas out there that would explain/resolve this problem