Home page doesn't come up in serps

home page on page 5 but internal pages fine

[The_Hitcher]

No quite come across this one before. One of my high ranking sites (was always a number one) no longer shows in Google searches for keyword searches on its home page although the page is indeed in the index. Internal pages (its a shop) all respond ok but its like Google just doesn't see the home page as even vaguely important - you have to really drill for it.

The site shows no obvious sign of being penalised and is in fact the most relevant and biggest site of its kind, now beaten on to page 5 by sites that are not only less relevant but extremely spammy ones. The site uses no heavy SEO at all, just a logical title and logical content but certainly should show first/second for keywords I'm inputting - has done for the last year.

This started around 10 days ago.

Any ideas?