Ron PAul thinks he got somewhat a of a fair break from the media in the beginning, (when most weren't paying attention anyway), but once the elections debates came on TV something changed. As other canidates starting dropping out he started getting less of a chance to speak then when all the canidates were in. The media did cover him less and less.
Some would argue that it's because no one was interested in voting for him, I think it's because his meesage was getting to too many people and the grassroots level was getting huge. I don't think some people liked that so there was a deliberate attempt to shut him up. Lets face it, without media coverage, you're fucked.