Ubuntu 13.04 installation does not detect Windows 7

I am trying to dual boot Windows 7 64-bt Professional with Ubuntu 13.04 64-bit desktop, but the installation can't detect my other Windows operating system.

My laptop is an Asus G75VW. It was preinstalled with Windows 8, but I erased everything on my hard drive and installed Windows 7.

My boot-info can be found here.

I had the same problem and found that it has something to do with the disk previously having had a GUID partition table but not completely wiping it out before changing to an MBR partition table. This results in an MBR partition table with corrupt GPT signatures, which gparted chokes on.

Before doing anything it's best to backup the current MBR, in my case Windows is installed on /dev/sda:

sudo dd if=/dev/sda of=sda.mbr bs=512 count=1

To clear the GPT signatures you'll need gdisk (apt-get install gdisk):

sudo gdisk /dev/sda

Switch to expert mode: x

To "Zap" GPT enter: z

The selection for the first question doesn't matter (MBR or GPT), be sure not to blank out the MBR.

Once you've done this you should be able to relaunch the installer and it will detect the partitions along with windows for dual-booting.