Unstable status of my Toshiba Transmemory USB

i am using 8GB Toshiba Transmemory USB. OS:Windows 8.1. OS shows the drive capacity and drive letter. but when opening asking for "Disk is not formatted". if "OK", trying to format and later "it could not be formatted". and the capacity becomes 0 MB. i tried many third party software, the results different as "insert the disk", "could not be formatted","0MB", "partition table invalid","write protected", etc. i tried diskpart also. it also failed to solve. and sometimes correct capacity part primary status heanthy and sometimes 0 MB unusable. it shows * in front of that partition. what does it mean. how can i format it. pl suggest.