If you're here, then I don't need to say that this solution will erase everything inside your Vita.
- Card doesn't detect at all, even restoring the defaults
- If you try to format inside the settings, it'll give you an error C2-12828-1 (AFAIK, it's a pretty much an old windows GPF, thanks for nothing, Sony).
- Even reformating the entire device, doesn't fix it.
- Enter in SAFE MODE (turn off the device, press power+PS button+R Trigger for some seconds).
- Format Memory Card (it will restart the device).
- Enter in SAFE MODE again, Restore the PS Vita, it will restart again.
- Enter in SAFE MODE for the last time and rebuild the database.