Hi, when i inserted first

Hi,
when i inserted first time My 8GB Transcend Pen drive, i was able to see & transfer contents from the computer to pendrive and vice versa..

but next time. if i insert it is showing (WINXP detects) it as a mass storage device, but when i click on it.. it says insert disk.

so please suggest the soluution as i have important data in that.. and i appreciate if the solution is without doing formatting..

Thanks..
Amar.