New domain or..?

Hello guys,
I have a site ( not a money site , a presentation site of my bussines ), i was first in top of google on my keywords. I made a blog ( site.com/blog ) and a store ( store.site.com ) .
I have used some fivver gigs and do some blackhatseo and then Google came with updates ( penguin ) and i lost my site ..now it can be found in fist 10 pages . I made another and another and tried to go on top with them . With one i've done it.

The problem is with store . I think he is not indexed well . I know some SEO , but something doesen't seems to be good because of domain witch is hited by penguin update.
Would be better to buy a new domain and move the store ? and the subdomain (store.site.com ) remain just a mirror , a redirect ?

Try continuing your current store with high PR backlinks. If you have a store, you might not want to lose your regular customers.

Its not that compulsion to buy a new domain as that makes your customer get away, My suggestion is...Penguin Recovery tool may help you... With that, you can remove all your irrelevant backlinks.. Either do that, or message google that not to consider those backlinks (which was gained through BH)..One more thing, i would like to ask you, do that "store.site.com" is a landing page or a shopping store????

Thx for answers . - Morty14 store.site.com - is a shopping store