I have an acer aspire 5610z, windows vista.I have been using my external without any problems. This morning when I plugged it in, it shows in device manager, but in my computer it doesn't show up. It shows in disk manager, but with no drive letter and I cannot access it. It shows online 232.88gb available and unallocated. I had another usb device hooked up this morning and I think that it took the drive letter of the hard drive and I need to assign another drive letter to it, but that option is not available. Any help would be greatly appreciated, thanks in advance