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You may have flashed the operating system for the Galileo to the SD card wrongly (if you did install one in the first place), or your SD card may not be properly formatted. Download SD Card Formatter and set it to be fully formatted, then if you want to install the O/S for the Galileo board, extract the downloaded files via 7z directly onto the SD card and it should start working.
If you're still having issues, try a different SD card.