You should be able to get the security questions for that account reset - all content that you download from the store is tied to the account that downloaded it, so it's generally best to only have and use the one account.
If you have a rescue email address (which is not the same thing as an alternate email address) on that account then the steps half-way down this page will give you a reset link on your account : http://support.apple.com/kb/HT5312
If you don't have a rescue email address (you won't be able to add one until you can answer your questions) then you will need to contact Support in your country to get the questions reset (these are user-to-user forums) : http://support.apple.com/kb/HT5699
When they've been reset (and if you don't already have a rescue email address) you can then use the steps half-way down the HT5312 link above to add a rescue email address for potential future use.
For the gift card, was it issued in the same country as you and your iTunes account are in (they are only valid in their country of issue) ? If it was and this page doesn't help then you will need to try contacting iTunes Support (you will probably need to give them images of the front and back of the card, and possibly its receipt) : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then iTunes Cards And Codes
