The pc is not detacting my Pen drive?

actually whenever i insert my pen drive in my USb port ,the pc doesnt detect it. I dont know what is the problem. all other pen drives are detectable but mine is not. my pen drive model is Transcend 4GB. I have a lot of data in it, can some body help me. Whenever the pc detects it the light will be on , but in my pen drive it never glows on.