For PC, redeem codes are different then serials

>If you have the code in this sequence ABCDEF-123-GHIJKL-456, this is a redeem code. which is plugged into here, http://preorder.na.finalfantasyxiv.com/
which generates a serial number that you plug into your Mog Station Account.
>If you have a code in this sequence 1234-ABCD-1234-ABCD-1234, this is a serial number which needs to be plugged into your Mog Station Account.

^^this is how i did it anyway, i dunno if this will work for you

If you have a serial number for ps3, you cannot enter it via website, it must be through PSN, and if it doesn't work its likely a problem with PSN and not SE.