Sudden traffic drop from Google - some content not being indexed anymore

I own a very popular blog called eGMCarTech (http://www.egmcartech.com) that covers the automotive industry. Through September 07 - December 07, we were getting a huge amount of Google traffic, about 3,000 - 4,000 visitors a day from Google to be exact. However for some reason on January 8th, our traffic dropped to about 500 - 600 a day from Google. We've been trying to figure out the problem ever since but can't find a solution.

Not only that, some of our new content does not seem to get indexed by Google. In the past when we used to write an article, it would be indexed within minutes, now we'd be lucky to get indexed at all.

Also, according to Google Webmasters Tool, we have over 1762 URLS that are in the NOT FOUND section and aren't being indexed.

Can someone from Google please help. We're dying here.
 
sad I’m frustrated
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