yahoo dropping our site like a hot potato

[dreamsarefree]

Hi, Hoping someone can enlighten me about the reason for Yahoo suddenly dropping our site off their search results. Our website always ranked very well with the top keywords related to our business, a few were no. 1 or at least the 1st. page. I was told by our "computer guru" that it had something to do with the search engine collecting data and should only be temporary. I was a bit sceptical as our site is the same as it was months ago when we ranked highly.It seemed to happen around the 15th. November, also our site was offline for nearly 24 hours on the 11th. and 12th. of that month. Unable to find reason for this. Is it just a coincidence with the timing or would this affect our ranking. Has Yahoo changed their criteria for higher results? Hope you can help. Thank you.