I have a website that sells a software product. My site used to be high up in search results on Google, Yahoo and Bing. Stupidly, I didn't do much with the site for about two months. It slipped in the Google search results, from near the top (and above the sites of a handful of competitors) to the second screen, but it completely vanished from Yahoo and Bing.
I can type in the name of the product, and it will then appear in Yahoo and Bing, but when I type in the keywords that describe what it does, only the sites of my competitors (and a bunch of random sites) appear. Odd, as if I type in both the name of the product and the keywords that describe it, it appears in Yahoo and Bing with the keywords highlighted, so it's thus still somewhere in Yahoo/Bing search engines.
Any ideas why this happened?
I am now spending more time updating the site, getting mentions of it on other online sites, etc. so that it will hopefully appear more.
Common reasons search engine result page results may differ from day to day, week to week.
To best keep track of your SEO positioning use something like Raven Tools
Other than black-hat SEO techniques as mentioned by @Ryan Doom; if you have not practiced any such techniques two months before when you last updated it then consider both on-page and off-page optimizations to help you get back your lost rankings in search results.
But above all, let me tell you that Google ranks search results based on relevance mainly. There are plenty of factors too but relevance to the search query is the prime factor. So while doing keywords analysis and research; keep relevance in mind and target only related keywords on related page(s) of your website. This will help Google to choose the best matching page from your website and rank it in SERPs on relevant keywords.
Your competitors have done well in those two inactive months of yours.
You need to build up your reputation with Google, yahoo and bing again.
Search engine just display those who justify those keywords, if your webpage justify it by a good active updatation. I am sure you will be back in business.