Your Google ad went inactive for one reason. The quality score was poor. You may have heard other factors caused it, but the quality score is the reason.

The initial quality score is determine by the relevance of your ad and landing page to your keyword. If you optimize both your ad and your landing page for the specific keyword, you should have a good initial score.

You optimize your ad by using the keyword in the ad. Put your keyword in the headline and/or the description. It's also a good idea to have the keyword in the URL of your landing page, which puts it in the destination URL. In addition, you can put the keyword somewhere in your display URL, since it won't affect the destination URL.

You optimize your landing page by applying the same techniques as Search Engine Optimization (SEO) would have you do.

* use the keyword in the page name or path path.
* use the keyword in the page title.
* use the keyword and related keywords in the keyword meta tag.
* use the keyword in the description meta tag.
* use the keyword inside "h1" HTML tags on the page.
* use the keyword throughout the content of your page.

The quality score is also affected by the ads CTR. As your ad gains impressions and clicks, AdWords computes your click through rate (CTR). AdWords draws conclusions about your ads relevancy from the CTR. Google assumes that if your CTR is high, above 0.5%, then your ad is relevant and your score goes up. Conversely, if your CTR is below 0.5% AdWords assumes it is not relevant and lowers your score.

An inactive ad has either an initial quality score that was poor that made it all but impossible to get a CTR and it went inactive. Or, the CTR for a good initial score is below 0.5% and it damaged the quality score to a point that the ad went inactive.

You have 3 options to fix the problem.

1) Delete the keyword. This is often a good solution because the poor quality of the keyword stops becoming a drag on the quality score of your entire campaign. Campaigns have a quality score based on all the keywords, so a poor keyword can damage the quality of other keywords.
2) Improve the quality score. This generally means improving the CTR by re-writing the ad sales copy to more persuasive. The more appealing the ad is to consumers, then more clicks you will get.
3) Increase your maximum CPC bid.