Ubuntu 12.04 can't see Windows 7

Question

I already read other questions like this but nothing seems to work. I just had my ASUS UX31A recovered from factory with Windows 7. Everything is fine there, so I tried to reinstall Ubuntu 12.04 LTS (the first time installation worked fine, so I was confident it would have worked this time as well). I shrik volume from my second Windows partition to make it unallocated, boot the Ubuntu live USB and when I try to install it tells me that there's no other operating sistem to install Ubuntu alongside. If I proceed with the manual operation to create the swap area and the OS partition, it doesn't make me choose whether it should be logical or principal, so I don't dare to go on. If I look at GParted it doesn't show the label OS on C:, while on the disk manager in Windows everything seems ok. What should I do? I DO NOT want to reinstall Windows, any other clue? Thanks

EDIT 1 I tried to launch os-prober in my Terminal and the only option I get is

/dev/sda5:Windows Recovery Environment (loader):Windows1:chain

while Windows 7 (mounted on dev/sda3) is not showed.

This is what I see in my Disk Manager inside Windows 7:

_{Click for a full-resolution image.}

(Sorry for the Italian Language, C: basically is the partition with Windows system's file, while the D: one is for data), while this is what I see when I launch GParted:

_{Click for a full-resolution image.}