Keyword Position Dropped

Normally if i search at google using the keyword "legitimate earning sites" i get the top position, that is ranked number One in the search results. Last night as i was browsing through google i was startled to discover that my website "Make Money Online" is no longer listed at rank 1 in the search results using the same keyword- Check this out! I am now ranked number 4 in the search results. I don't know why it happened, why the sudden drop. I did change my templates a couple of times. I wonder if it caused the sudden changed or could it be that i changed the metatags? What is more confusing is that if i use the SEO keyword Position Checker my website is ranked 1, 2, 3 using the keyword "legitimate earning sites".

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Compare the results:

• Now at Google -Make Money Online is ranked 4
• SEO Checker- Make Money Online is ranked 1 and 2 (Which had be the case normally in the past weeks)

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I don't really know what's the real reason for all of these. I do understand that page rank or keyword position is a complex matter and that there is competition in the net in relation to this. Well, another website/s may have outranked me.I just hope i can keep my website on the top again, consistently everytime someone uses the keyword "legitimate earning sites". (Sigh!)