Hey JamesW123. I'll need a bit more specific info than that. Where is the sd card not recognized - Windows Explorer, Disk Management, Device Manager? How did you try to format it - with your phone, computer or another device? I'd recommend that you try the card with another device to see if the same thing happens. I'd recommend that you check the manufacturer's website and see if it offers a formatting tool which you could try.
Hope that helps.
Boogieman_WD