I think a lot of the answers here make a lot of sense, and you should consider doing them if the following does not work, but I am nonetheless apprehensive about them because of the dramatic drop to nearly zero. This indicates that your usual visitors (that would normally visit your website without google searching for it) are not getting registered.

The first step I would take is check whether your tracking code etc. is corrupted, removed, or hacked. Then, remove filters and log on to the site yourself and see whether it registers.

It is quite unusual, even if you're penalized by Google, for it to go down to zero from 1000.

Keep special care of your keywords on Index page. Write articles and blogs which are authentic and insert those keywords within first 150 words and last 100 words. Do not put more than three keywords in your content.

Also make good use of your links like by giving genuine comments on relevant sites and to ease with this you can hire an SEO expert.

The drop is sudden. High chances are that your website has been penalised by Google due to latest update. Consult an SEO expert who can help you to recover. Here is one the service you can try to recover from penalty. http://goo.gl/MItaOp

Check for any warnings in your webmaster tools. Then diagnose using the flowchart found here:

http://moz.com/beginners-guide-to-seo/my...

scroll down to the bottom to the subheading: so how do you know if you've been bad?

i think u may change your site content or meta tags

and do relevant off page only

I have a problem with a lot of my keywords which were previously on pages 1-3 on Google but then just disappeared from Google completely a few weeks ago.

why it's all happening and what's the solutions?

Here is my site analytics report: http://i.imgur.com/gqayyh1.jpg