I have two internal hard drives. One is 1TB and the other is 1.5TB. For some reason when I am using Windows for a while the 2nd drive will disappear from My Computer. I will be downloading something or doing nothing and all of a sudden it goes away. I restart my computer and during the reboot it will reappear. I will go back to using my computer for a day or so (sometimes its less than that) and it disappears again. Please let me know what additional information you need so I can stop this from happening.