Hey there, Madhu.
The SD card might have failed, just as @xpcman has suggested. However, there are some thing you could still try before you completely give up on it.
Try formatting it with a different computer or device, to see if the same thing happens. You could also try downloading its manufacturer's formatting tool (most SD card and flash drive manufacturer's offer such tools for their devices), to see if it's able to reformat the card and if you can use it afterwards.
If nothing seems to work, perhaps the memory card has failed and you should be able to get it replaced by contacting the vendor you got it from, if it's still under warranty.
Hope that helps.