Problem while formating kingstone 4GBpendrive

Hello,

I just bought a kingston datatraveler 8gb. I have just used it to store a backup of my files. When I reinsert it on the computer, the flashdrive display a message of being not formatted, I tried to format it but it can't be formatted. I tried to look what file is on the flashdrive but it appears that there has no capacity display on the drive. Pls. help.