Just to make sure I understand, Mint looks like it's installing properly, but doesn't seem to be there on reboot? I must say I have never encountered this and I did once successfully install Mint 64-bit to dual-boot with Win7--it went very smoothly.
To get started, two questions which are both sort of stabs in the dark:
Where did you install Grub?
From the Live CD, could you open a terminal and, as root, run the command
to generate a listing of the partitions? Post the output here, being sure to surround it with "code" tags, which become available when you click the "Go Advanced" button to the right of the "Post Quick Reply" button at the bottom of the reply window.