I am having a blog which is based on mixed categories. From 4th of jan i have lost my page rank to 0 from 3. I have read fourms here and found that your rank effect by your bad backlink and other problems too. My question is how do we know that which is bad backlink and how we can remove it from the websites where we have posted them.
There are three tools I use for most of my backlink checking, Yahoo Site Explorer, Open Site Explorer, and Google Webmaster Tools.
check this http://www.searchenginejournal.com/how-to-guide-on-identifying-bad-links-and-pruning-them-using-googles-disavow-tool-by-navneet-kaushal/51372/ but you will need also a service like the one at ahrefs.com to determine bad links so you can use disavow tool after
they won't tell you which bad backlink is the real affect on your SEO result. But you can find all your backlinks you have made in google webmaster tools -> links to your site. You also can use the latest Disavow Tool to tell Google to ignore or not index on which backlinks.