Long story short, I just recently reinstalled Vista x64 and formatted my C drive. I built my system about 16 months ago with 2 hard drives, I added two more 2 TB drives about 3 months ago. I now have a WD 640 GB drive which I bought when I built my computer, a 500 GB seagate drive that I bought about 2 years ago and transferred it to the new system and two 2 TB Samsung drives. All drives are internal and are assigned letters.
I have always been able to hit the sleep button (with the crescent moon icon) on my keyboard and it would put it into sleep mode. I would have to hit the power switch to get out of sleep mode because the keyboard wouldn't take it out. Everything worked fine.
After formatting and reinstalling this week, after I come out of sleep mode both of my 2 TB drives disappear and can't be accessed. Even under disk management. When I restart my computer they reappear. I have checked the connections and they seem fine. I have also changed the power settings so that my hard drives don't turn off. I can't understand why two of the drives would disappear but the other two would remain.
Can somebody please help me with this because it is very frustrating.
Check your ATA drivers (in Win 7 64 device manager under HDDs). If it's the Microsoft drivers showing for your hard drives, go to your motherboard manufacturer's/computer manufacturers site and download the drivers for your chipset.
I had the same problem and tried installing the ASUS P6T chipset drivers and my problem has now resolved. I can resume from sleep with all HDDs present.