Are you using the right type of SD card? Check the manual. My guess is that you need no more than a Class 4 SDHC. It may not like the newer, larger, faster cards. For awhile, the most common cards were 32GB Class 10 and they have become pretty cheap.
Also, could it be the tiny plastic write protect tab on the card is in the "off" position?
It is also possible that you have a format issue. I think smaller cards prior to 64GB are "FAT32" and later, larger cards are ExFAT. Have you tried a smaller Class 10 card and doing a complete FAT32 reformat in you computer and then a camera format?