I had one old adwords account 6 months old account which was unused, i added cc to it, but i think i couldn't enter promo code of $100 which i got from hosting company because account is too old. so today i created new adwords account so can i enter same credit card to this account? + reps for any answers thanks
If I remember well it didn't work. What I've done before is getting a second credit card number on the same account for a relative (with is permission!) and I use that number if needed. Most credit card companies allowed that for free, or a small fee. Prepaid credit cards works well too, if you grab a rechargeable one. That's what I use anyway on my AdWords campaigns.
AdWords promotional coupons, when legitimate, are meant to be used one per new advertiser, for their first and only account. Since you are using CC with your older account and if you use the same CC with the new account, Google will come to know that you are not a new advertiser, that can put you at serious risk of having all accounts permanently shut closed by Google, including the original account.