I had a similar and strange thing happen. I am a total newbie, though learning fast. I set up my adword account and immediately set up my first campaign. And received about 30 clicks the very first day which landed me my first sale and a profit of over 100% on investment, then a rapid decline to nothing. 1 or even zero clicks a day. I just let the account ride, planning on killing it when my profit had been eaten up, then suddenly after about 2 or 3 weeks the clicks started to soar to about 450 a day and my sales started coming in quite nicely. making a profit of about 50% - 150% a day. with a few days of small loss, but over all a nice profit for my first affiliate product experiment. I should mention that I am getting most of my traffic from contextual adds. That campaign uses a huge list of keywords (1000's). Last night I set up a copy campaign for the same product but with a very refined list of keywords, bidding much higher amounts for valuable keywords that I wasn't previously willing to pay for, still including contextual advertising. I landed a sale within 2 clicks but am now at 30 without a second sale. Too new to tell what is going on. I am still not even sure if the first campaign is a fluke yet, as it only took the upturn about 2 weeks ago. Anyone know what might have caused that slowing down then rapid surge without any change to my campaign?

It can depend on a number of factors. For example, how much competition is there for the same keywords? Do your ads stand out from others? Has your position fallen? Are other advertisers using the same URL? If they are, Google will usually only display the add with the highest bidder. You need to find out it you are still getting impressions - if not, your ad may not be showing.