it's really hard to answer that question, i lost it a few times, and had to reinstall SME 2 of those times, once i was lucky that after i rebooted it all worked fine (thanx to the template system in SME)
the last time i killed my server-manager i was using proxypass, and made a mistake, a bad mistake
there was a warning with proxypass not to leave one of the fields (can't remember which one) blank, or it would just forward, and you loose all access to your server via http, and that needed a reintall
anyway, if you could give a little more info on what was the last thing you did or installed, what contribs you had installed, and last what version of SME was installed.
cheers