I am very frustrated and angry since i recently changed my template of my blog and found after a couple of days that my blog disappeared from the google index. My blog was pr 3 blog and i wanted to change the theme of it and changed it and now i am not indexed at all. what should i do to get it back?

Change the template back. Other than that and given the (lack of) information you have provided:
Absolutely no idea

Have the page names changed?
is the navigation now in javascript?
do all your internal links have a nofollow value?
is there a robots meta in the pages?
are you blocking bots by some other method?

plus a myriad of other questions

how about you tell us where we can see this problem for a start.

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