If you use AdWords and use the desktop AdWords Editor application you may need to double check the settings. I have noticed recently that some of the settings for a campaign within the Editor do not update my AdWords account. For example a new campaign created in the Editor was set for the content network and Relevant pages across the entire network, after multiple uploads of changes it was never sent to AdWords. When I looked in the campaign settings it was set to Relevant pages only on the placements I target. Obviously these are two completely different settings.

Double Check AdWords in the Browser
I strongly suggest you double check campaigns and campaign settings. I only noticed the discrepancy after a particular campaign was not yielding any impressions. At first I assumed it was just my fault, however that exact same issue has happened multiple times. Be sure to double check your settings and other campaign components.

Google AdWords Editor
If you do not use the editor I highly suggest you give it a try. The AdWords Editor is a software application you download for free from Google. It is very powerful, allowing you to set up campaigns, make editors, copy, paste and provides more management functionality than using AdWords through the browser. It also allows you to manage multiple accounts and manage accounts offline, you can make edits to campaigns and upload whenever you like. Get your free copy of the AdWords Editor from Google.