How to make a new card work

What type and size memory card? The CX4230 works with MMC and SD cards, 2GB or smaller. It will not work with higher-capacity SDHC cards.

The camera uses SD cards. I assume your new card is 8GB, not 8MB as you stated. If this is the case, it's an SDHC card. While it fits into the slot, it is electronically incompatible and will not work in the SD-only camera. You need to use SD cards, 2GB and smaller.
You may download a copy of the manual here.

The P880 works with MMC and SD cards. Your new 4GB card is an SDHC card. While it fits into the slot, it is electronically incompatible and will not work. The camera is limited to working with cards 2GB and smaller.

The DX6490 works with MMC and SD cards. While an SDHC card will fit into the slot, it is electronically incompatible and will not work. Some Kodak cameras can use SDHC cards, but the DX6490 is not one of them. You need to go with SD cards, 2GB and smaller.

It's possible your camera can't use a 4gb card.

camera

You need to format new cards in the camera before using.

Have you tried formatting the new cards in the camera before trying to use them?

No, it should work fine with the new one. If it's not working, make sure the card isn't locked. If its still not working, make sure the card isn't full and if that doesn't solve it, I would advise to get a new card.

I had the same problem and downloaded a firmware upgrade from the Fuji web site and it now works in the camera.