A few years ago, I was having a problem like yours and it turned out that an anti-virus program had disabled automount. The fix for my system was: Open a command prompt with administrator privileges. Or in your case, from Win RE.
type "diskpart" (without the quotes) and press enter.
when the 'diskpart' prompt appears, type: "automount enable" (again without the quotes) and press enter.
"exit"
I don't remember if a reboot was needed, but it wouldn't hurt
Good Luck, I hope this helps.