Some anti-virus software stops bliss starting its user interface. Known examples of this are Avast! and some Norton/Symantec anti virus software. In these cases, try disabling the anti virus software for a short period to see if the problem is rectified. If it is, you need to disable the setting that stops software starting a web server. In Norton, this is called Default Inbound Loopback.
Any other FAQs I forgot or clarifications required? Post your ideas below!