When the card worked before, check if you did not switch the lock switch down. And check all contacts on the card and in the camera. They should be clean and shiny. When you recently bought a new card you could have bough a SDHC card and these won't work in your S800. The S800 only accepts MMC and SD cards, The SDHC and SDXC cards won't work. A few years ago you still could buy 4 Gbyte SD cards. Now even most 1 Gbyte and 2 Gbyte cards are already SDHC. SDHC was introduced at least 7 or 8 years ago, so all new devices accept SDHC. The SDXC was introduced at least 4 years ago, so in a couple of years, you perhaps only can buy these cards?
Answers & Comments
When the card worked before, check if you did not switch the lock switch down. And check all contacts on the card and in the camera. They should be clean and shiny.
When you recently bought a new card you could have bough a SDHC card and these won't work in your S800.
The S800 only accepts MMC and SD cards, The SDHC and SDXC cards won't work.
A few years ago you still could buy 4 Gbyte SD cards. Now even most 1 Gbyte and 2 Gbyte cards are already SDHC. SDHC was introduced at least 7 or 8 years ago, so all new devices accept SDHC. The SDXC was introduced at least 4 years ago, so in a couple of years, you perhaps only can buy these cards?