If I type in a search in google.com and there is ONE ad on the right of the search results page, does that mean only ONE advertiser is paying for that keyword (and, likely, a low amount)? If there are NO ads, does that mean NOBODY ahs bid on the keyword, or that those who have bid ran out of money, and therefore are likely not big players? I searched for some things earlier, and was surprised by getting both of these results.
It could be that the term you typed in is also a trademark, which means Google wont let you bid on that term. It happens quite a bit.
Also if it's a very general term like 'computers', it may be that advertisers are unable to maintain a high enough click through rate for Google to allow their ads to run.