Did it disappear for a certain keyword or for all keywords?

Does your site still show when you type in just your domain? mysite.com

I wouldnt be to worried if it just happened. Give it a few days and it doent return to its previous ranking check Google as posted above.

If you can still find your site within google (site:domain.com) then it's just the google dance, if you cannot find your site within google, you've been sandboxed, either way the best way to trackle these two issues, is to carry on building backlinks, adding content and just working on the website.

If it just disappeared with all keywords, then it may mean that your site has been punished by Google.
Just wait a few days and watch that if it returns to the previous ranking. If it doesn't return, then you should take some measures to let it recover.

Just give it a day or more. I've also experienced that before and I feel the same as you. Don't worry to much just continue optimizing your site.

Maybe all the links from SEO activities you worked on have been discovered and removed by the websites and forum admins, accordingly removed from GG. Then your site is still exists in GG but all the links to it have no longer existed.

I have been working on my site for a month and was excited when it showed up in the first 250 listings and then it disappeared, when it came back it was like 300, then disappeared for about a week. Recently is resurfaced at 158 before disappearing again.

Do yourself a favor and just stop looking for it. The google dance, as they call it can drive you mad.

Recently Google has updated the page ranks, and we have seen the certain improvements in the page ranks and same decrease in page ranks too.

Few days back google updated the Page rank so that might be the reason.

ronmojohny, thanks for the further instruction. I don't think I understand how to use these queries, as my site is invisible when I search run either search and after a few tries I got a "google - sorry..." message saying my computer or network may be sending automated queries...can't process request right now.

If you know of any other resources I might use to diagnose and ultimately fix my damaged ranking numbers, I'd really appreciate it. Meanwhile, thanks again and have a great night.

It might be some technical reason..Don't worry you will get back your position...