First, you should know this is a customer to customer forum and, while DreamHost staff occasionally drop by, they rarely post here. If you have an issue you wish to discuss with DreamHost, you should use the appropriate channels for that: filing a support request in the control panel, replying to a tech support email, or using the contact form at http://dreamhost.com/contact.cgi.
In reply to:
I have 2 account on Dreamhost ... The second account I registered used reward coupon of the first account and now I get both account banned and they said they will not refund me..
That sounds about right to me, from what you have described. By using the promo code from your first account when you opened your second account you fraudulently obtained a discount that you were not entitled to receive (you were *not* a new or "first-time" customer).
In reply to:
I don't know what prevent me to register many accounts on Dreamhost, just think each account should be treated as a new customer.
Well, the TOS prevents you from opening multiple "plans", and warns that all plans will be terminated if you do (See paragraph 8 under Material Services)"
"The Customer agrees to hold only one (1) active web hosting service plan at any given time with DreamHost Web Hosting. Signing up for multiple plans is grounds for termination of all plans, including the first one, without warning."
That said, there *is* a way to "add accounts" from within the control panel, and they allow you to do that for accounting reasons, but *not* to do it as a "new" signup with a promo code discount. 
In reply to:
I need an explanation from Dreamhost and hope to get my sites reactive soon.
You should seek any further explanation directly from DreamHost; I don't know how anyone *here* can help you.
As for getting your account(s) re-instated, I cannot speak for DreamHost, but I would be very surprised if the continue to business with you after having terminated your account(s) as you described.
I can understand that you are unhappy about not being able to continue to host your sites on DreamHost, but if it were me, I'd just move on and find some new hosting as soon as possible. 
--rlparker