Memory Card Issue

my memory card which i use on my nokia phone suddenly is not read on my mobile. when i plugged it to my notebook using a SD card reader, it shows for a couple of seconds then disappears. im unable to format it at all... it keeps showing then disappearing and i doont know how to get it to stay there, it does the same thing on my mobile. so im not able to format it on my phone. i dont know what to do to fix it. plz help