Help, my website is suddenly not ranking on Google

my website up until last week was one of the best ranking websites for all the suburbs in my capital city with respect to patios and carports. I did this buy adding a tag for each suburb and using the tag page to effectively make a different page for each suburb. Another site did this and they rank great too (we were 1 and 2). Suddenly my site has fallen off the earth as far as Google goes. Nothing appears to have changed EXCEPT google found a few hundred old url craml errors since the old sitemap. could that cause it? would the tags pages cause it?