external drive

I recently purchased an external drive{500gAcomdata model}It worked fine for about a month with Windows xp. windows suddenly stopped showing the drive in My computer.I tried rebooting and changing usb ports but that did nothing. I left the power off for awhile and it finally started showing in My b computer but as a cd drve only, which I cannot access!I even re-installed the windows xp twice. The explorer recognizes the drive only as a cd drive. What else can I try?