Windows 7 may exhibit a variety of issues when waking from sleep. One of the more recently reported issues involves the disappearance of mounted internal or external hard disks when the system is put to sleep (hibernation)–usually hybrid sleep–then woken up.
This issue will likely be resolved by a future update to Windows 7 or new Windows 7-compatible disk driver updates. In the meantime, there are two potential workarounds:
Disable hybrid sleep First, you can simply disable hybrid sleep by going to Power > Advanced > Sleep and turning off “Allow hybrid sleep.”
Turn off SATA Enter your system’s BIOS mode. This is accomplished by pressing a specific key repeatedly as soon as your computer is turned on (or right after it is restarted). For many computers, the key is F8, but it may be F1, F2, F10, the Delete (del) key or the Escape (ESC) key. Consult your computer or motherboard’s manual or try different keys until you find the right one.
Next check your HDD or storage settings. Turn off SATA and reboot normally.