I have never heard of a 8 gig SDXC memory card.
All SDXC memory cards are 64 gig and larger capacity.
I assume you have a SDHC memory card.
SDHC memory cards are 4 gig through 32 gig capacity.
All SD memory cards should be formatted with the CAMERA before taking pictures.
If you did not do that ... do it now.
Formatting a memory card will delete all pictures on the card, so make sure you copy (to your computer) all pictures on the card before formatting it with the CAMERA.
Things to avoid:
If you have a card reader on your computer, it is OK to use it to copy pictures to your computer.
But:
You should not write to the memory card with the computer.
You should not format the card with the computer.
You should not delete pictures from the card with the computer.
..
My Panasonic Lumix had no problems with it's 8 gig SDXC card, then one day...BAM! Didn't recognize it! But my computer did!
The next day, out of nowhere, the camera recognized the card again!
Should I send the camera for repair while it's still under warranty?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic