Never unplug it without safe removal or your card would report error like 'not formatted error' next time when you connect it to pc.
if you want to format it directly, try the following:
1, get it connectted to pc and go to disk management, right click the card which might appear like H or F or some other. Go to format option directly
2, if the first option failed, try a formatted here and i am sure it would work for you http/panasonic.jp/support/global/cs/sd/download/index.html