Update: If boot-repair fails and you want to reinstall the system to make a the dual boot work, you can follow this steps or look at the official guide here: https://help.ubuntu.com/community/WindowsDualBoot
- Run Ubuntu and backup your files from the NTFS partition.
- Download the GParted Live ISO. Architecture dependant.
- Burn the ISO from 1, using a burning tool or create a bootable usb drive (http://gparted.org/liveusb.php)
- Boot the CD or USB drive
- Delete the Entire Disk Partition.
- Create A Windows Partition, of desired size, type NTFS, and Label it windows (be sure that it is primary partition because the windows boot-loader need this).
- Create an ext4 partition of at least 100MB for /boot, and label it boot.
- Subtract your RAM from the amount left.
- Create an ext4 partition of size (Total Size - Amount in step 8), label it root.
- Create a Swap Partition, size should be at least size of your pc memory (RAM).
After Partitioning the Disk, reinstall Windows, using the NTFS Partition created in Step 7, making sure to use the option to preserve the existing disk format.
After the Windows Install completes, reboot the computer with a Ubuntu ISO, click install, and choose something Else. Make sure to follow your labeling scheme, i.e. mount / on the partition labeled root, mount /boot on the partition labeled boot, mount windows on the mountpoint named /windows and mount swap. Make sure not to format the partitions
Save the custom layout, and continue the installer. When asked to install GRUB install it in the partition mounted as /boot. The installer will detect the Windows Install using os-prober, and add it to your GRUB Menu.
Lastly, Do not use WUBI