Jen ~

It's quite possible the loss of battery power (when the broken
battery door acts up) *IS* the cause of the memory card failures.

I'd start with going back to where you purchased the New Memory Card
and telling them "It doesn't work" and that you'd like a refund.
IF they have a policy of "no refunds on electronic stuff" -
you might have to deal with the card's Manufacturer - and
THEY will probably only be willing to "replace" the card.

Before you try ANOTHER memory card in that camera - you should
contact the Camera Manufacturer - and ask how much $$$$ they want
to repair the battery door.

Good Luck!

/s/ Phred