The most common reason that the site Title doesn't show is that the theme you have selected requires the Title at the top be a Logo Image. Some themes display the text and others require a logo.
In general, most of the StudioPress themes will display text and most of the Elegant themes will require a logo.
You can either select a different theme or use one of these services to create an image logo.
(free online image editor) http://apps.pixlr.com/editor/
Many of these are free to design your logo, then you pay for the final product...
You can even try a service like www.fiverr.com