Re: While installing Unplugged theme for BP it gave fatal error!!
The fatal error you are receiving is probably from not disabling buddypress linked plugins and THEN the actual Buddypress plugin itself BEFORE upgrading (Read more here – https://codex.buddypress.org/getting-started/upgrading-from-10x). I have crashed my site in the past from doing this. My theme itself really only has minor code changes and it’s not really possible to crash a whole site as it takes most of the code from the default theme.
The Unplugged theme also works ONLY with Buddypress 1.2rc+ and WordPress 2.91+. Installing Buddypress on a wordpress website in general may be a steep learning curve at the start but please read all the instructions on that link to guide you through.