My mainpage never get ranked??

I'm trying to rank my client's site for medium competition keyword. But strangely after all efforts done, the homepage never got ranked, not even in top 1000. Instead the inner page unexpectedly got ranked in 2nd and 3rd page (which I never do anything).
Some other inner page got ranked 200th something (page #20). But I can't see the homepage??

Does anyone have any idea what happen here? The mainpage definitely has better onpage optimization than the ranked innerpages.
And yes the homepage is indexed in Google. The domain age is 1+ year old.

I don't think Ive "over-optimized" or done any massive spammy links. What I did just some press release, web 2.0, few manual blogcomments, few article submissions, etc. Never did any xrumer or scrapebox directly to the homepage. It's been more than 4 months since I start this project and there's not much improvement. I had to persuade my client so that I would rank his inner pages, but (as I expect) he was reluctant.

I've done some SEO projects but never met something like this before. I would appreciate if there are some experts here willing to share their experience with this kind of situation.

Could be a content related issue? Is the content unique?

it happens to me too but its good for me as i have tutorial sites

CaseAndPoint said:

Could be a content related issue? Is the content unique?

Click to expand...

The website is an online store. And there's not much text content I have to admit. But it surely still have more than the ranked innerpage. The innerpage is just products pictures, price, and very little text content.
And yes the content is unique. From any point of view the innerpage shouldnt deserve to rank higher than the mainpage itself.
The problem here is that the mainpage is indexed but nowhere to rank for any keywords.