Does Windows recognize the 720? If yes try to select "exFAT" under File System when you run Format. I was able to "wake up" the internal memory on a cranky TT using exFAT. You then should be able to format with FAT32 if you want. If that doesn't work there's lots of freeware format tools out there you can try, SDFormatter for one.
Good luck. The 720's are notorious for bad memory chips.
my go 520 internal hard drive cannot be recognised by the computer, it comes up as a drive when plugged into the computer but when i try to reformat it, it says please insert a disk and try again. I tried the sdf formatter but it won't pick the drive up. only the sd card inserted. Any ideas how i can get the computer to recognise it to enable a reformat?. It went on me when trying to reformat and came up with a error saying format failed. since then it won;t recognise it as a drive properley and i can't access it at all. Anybodys help would be appreciated.