Not too sure about pokerstars but but most US credit cards have restrictions and won't let you deposit at any gambling site. I tried before at other sites with no success, you would have to try an alternative method. Some sites will take a bank debit card though, I think like Cake and Carbon, not too sure about others. Hope this helps a little.
In canada I'm using an prepaid electronic Visa card issued from Money Mart, it cost me $2.00 cdn to reload the card and all the poker sites I play at including PS accepts this method of payment. Like I said I'm from Canada so you'll have to check down there if it will work the same way.
Are you in the US though?
As far as I know no pre-paid cards are accepted anymore, if anyone knows of any pls pm me.
The best options are echeck, or mailing a money order or bank check, western union but there are fees.