I was helping a friend remotely to dual boot Ubuntu with Windows 8.
He installed Ubuntu to /dev/sda7 and when it asked for where to put the bootloader, he selected the same (/dev/sda7)
When he rebooted, windows automatically boots, no GRUB menu.
How do we fix it to re-install grub to /dev/sda or /sda1 (whichever is required)
Bug https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1396379
was active at this time, and your user input was likely ignored (on your unspecified release). Grub installs to the first EFI the installer finds, so try the EFI boot menu (some key at powerup to select device/os to boot) and select ubuntu. Rearrange boot order to put ubuntu first if that works. Your unspecified hardware may have other problems, like having to set "trust" on Acer bootloaders.
The simplest thing to do would be to simply reinstall, choose "something else", pick the existing / and swap partitions, and leave the boot loader set to install to the default of /dev/sda.
It would be easiest to reinstall as you have no data. Start by formatting that partition in windows and installing how you did before. Ensure you select the right drives. Formatting probably isn't necessary.
All is not lost. The grub loader should be installed to /dev/sda. I just wrote this up the other day here. It should still work for your case.
